Semiconductor device and method for producing semiconductor device

ABSTRACT

Provided are: a semiconductor device in which a non-volatile switch provided with a rectifying element and a non-volatile element provided with no rectifying element are formed in the same wiring; and a method for producing the semiconductor device. The semiconductor device includes a first switching element and a second switching element disposed in a signal path of a logic circuit. The first switching element includes a rectifying element and a variable resistance element. The second switching element does not include the rectifying element but includes a variable resistance element. The first switching element and the second switching element are formed in the same wiring layer.

TECHNICAL FIELD

The present invention relates to a semiconductor device and a method forproducing the semiconductor device and particularly relates to asemiconductor device that is used in an electronic device, such as aprogrammable logic and a memory, and is provided with a variableresistance element using deposition of a metal and a rectifying elementand a method for producing the semiconductor device.

BACKGROUND ART

In order to diversify functions of a programmable logic and promoteimplementation of the programmable logic in electronic devices or thelike, it is required to reduce size of each switch connecting logiccells to each other and reduce on-resistance of the switch. It has beenknown that a switch that uses deposition of a metal in an ion conductivelayer in which metal ions are conducted has a smaller size than aconventional semiconductor switch and has a small on-resistance.

Such switching elements include a two-terminal switch disclosed inPatent Literature 1 (PTL1) and a three-terminal switch disclosed inPatent Literature 2 (PTL2). The two-terminal switch has a structure inwhich an ion conductive layer is interposed between a first electrodesupplying metal ions and a second electrode supplying no metal ion.Switching between both electrodes is performed through formation anddisappearance of metal cross-links in the ion conductive layer. Sincethe two-terminal switch has a simple structure, a production processthereof is simple and easy, and the two-terminal switch can be processedto a small element size in the order of nanometers. The three-terminalswitch has a structure in which second electrodes of two two-terminalswitches are integrated into one electrode and is capable of securinghigh reliability.

For an ion conductive layer, a porous polymer including silicon, oxygen,and carbon as main components is preferably used. Since a porous polymerion conductive layer is capable of maintaining a breakdown voltage at ahigh level even when metal cross-links are formed therein, the porouspolymer ion conductive layer excels in operation reliability (PatentLiterature 3 (PTL3)).

In order to implement a programmable logic with such switches as awiring changeover switch, it is required to increase density byminiaturizing the switches and simplify a production process. Wiringmaterial of a state-of-the-art semiconductor device is mainlyconstituted by copper, and a method for efficiently forming a variableresistance element in copper wiring is expected. With regard to atechnology for integrating a switching element using an electrochemicalreaction into a semiconductor device, a two-terminal switch using thetechnology and a three-terminal switch using the technology aredisclosed in Patent Literature 4 (PTL4) and Patent Literature 5 (PTL5),respectively. According to the literatures, a technology for using acopper wiring also as a first electrode of a switching element on asemiconductor substrate is described. Use of the structure enables astep for newly forming a first electrode to be eliminated. Thus, a maskfor forming a first electrode becomes unnecessary, and the number ofphotoresist masks (PRs) to be added for producing a variable resistanceelement can be reduced to 2. On this occasion, since film-forming an ionconductive layer (a second ion conductive layer) directly on a copperwiring causes the surface of the copper wiring to be oxidized andleakage current to be increased, a metal thin film functioning as anoxidation sacrificial layer is interposed between the copper wiring andthe ion conductive layer. The metal thin film is oxidized by oxygenincluded in the ion conductive layer and becomes a portion of the ionconductive layer (first ion conductive layer). A metal constituting theoxidation sacrificial layer forms an alloy layer at a boundary face withcopper, and, when metal cross-links are formed by voltage application,the metal is incorporated into the metal cross-links.

Non Patent Literature 1 (NPL1) discloses that improvement in thermalstability of metal cross-links by the metal having diffused into themetal cross-links causes retaining resistance (retention) to beimproved. On that occasion, since incorporation of the metal into metalcross-links causes generation efficiency of Joule heat to be improved,required current at the time of transition from an on-state to anoff-state does not increase.

To wiring changeover switches in a programmable logic, a crossbar switchstructure in which switching elements are arranged at intersectionpoints between wirings is applied. In the crossbar switch structure, atleast one select transistor is required with respect to each switchbecause of inhibition of sneak current at the time of signaltransmission and current limitation at the time of selection(programming). For this reason, there has been an issue in thattransistors occupy a large area and an advantage of a small-sized switchcannot be fully exploited.

Thus, Patent Literature 6 (PTL6) discloses a structure in which abipolar rectifying element is arranged on a three-terminal switch.Programming of the three-terminal switch is performed through therectifying element, and current at the time of writing is limited by areached current through the rectifying element. In addition, therectifying element inhibits sneak current to an adjacent element via thecontrol terminal of the three-terminal element, which prevents anerroneous writing from occurring.

CITATION LIST Patent Literature

[PTL1] JP2002-536840A

[PTL2] WO2012/043502A

[PTL3] WO2011/058947A

[PTL4] JP5382001B

[PTL5] WO2011/158821A

[PTL6] WO2014/112365A

Non Patent Literature

[NPL1] Tada et al., “Improved ON-State Reliability of Atom Switch UsingAlloy Electrodes”, IEEE Transactions on Electron Devices, Volume 60,Issue 10, pp. 3534-3540, 2013

SUMMARY OF INVENTION Technical Problem

However, the semiconductor devices described in the background art havean issue as follows.

In the multi-terminal switch structure provided with rectifying elementsdescribed in the background art, rectifying elements are formed on allswitches. Although it is preferable to replace a power supply linesupplying power source to a programmable circuit constituted by crossbarswitches, such as a multiplexer and a lookup table, with a non-volatilethree-terminal switch, such a non-volatile three-terminal switch isrequired to cope with various voltage levels and current levels andsecure high reliability. However, since a current limit level by arectifying element is determined invariably by film thickness of arectifying layer, it becomes impossible to adjust a resistance level ofthe switch. To secure reliability, a switch is required to have a lowon-resistance, and it is preferable to perform current control of athree-terminal switch on a power supply line by use of a transistor.Although it is possible to increase a current limit level by increasingarea of a rectifying element, a current level that was determined oncecannot be changed in the rectifying element and fine tuning at the timeof circuit operation (for example, adjustment of power supply voltage inassociation with a change in an operational frequency) cannot beperformed.

In addition, when a multi-terminal switch provided with two rectifyingelements and a three-terminal switch are integrated in a multilayerwiring layer in accordance with the background art, photoresist masksfor patterning respective structures of the multi-terminal switchprovided with two rectifying elements and the three-terminal switch arerequired. As a result, the number of exposures increases, which causes aproduction cost to increase.

An object of the present invention is to provide a semiconductor devicein which a non-volatile switch provided with a rectifying element and anon-volatile element provided with no rectifying element are formed inthe same wiring and a method for producing the semiconductor device.

Solution to Problem

To achieve the above-mentioned object, a semiconductor device accordingto the present invention comprises a first switching element and asecond switching element that are disposed in a signal path of a logiccircuit, wherein

the first switching element includes a rectifying element and a variableresistance element,

the second switching element does not include a rectifying element andincludes a variable resistance element, and

the first switching element and the second switching element are formedin the same wiring layer.

A method for producing a semiconductor device in which a first switchingelement and a second switching element are formed at the same time, thefirst switching element including a rectifying element and a variableresistance element, the second switching element including no rectifyingelement and a variable resistance element, the method comprises:

film-forming electrodes and a variable resistance layer that form thevariable resistance elements;

film-forming electrodes and a rectifying layer that form the rectifyingelement;

forming a first pattern for constituting the variable resistance elementand the rectifying element to a hard mask for forming the firstswitching element;

forming a second pattern for constituting the variable resistanceelement to a hard mask for forming the second switching element; and

etching the rectifying layer and the variable resistance layer at thesame time by use of the hard masks to which the first pattern and thesecond pattern are formed.

Advantageous Effect of Invention

According to the present invention, it is possible to achieve asemiconductor device including a non-volatile switch provided with arectifying element and a non-volatile switch provided with no rectifyingelement in the same wiring in a multilayer wiring structure. Accordingto the present invention, it is also possible to form a non-volatileswitch provided with a rectifying element and a non-volatile switchprovided with no rectifying element in the same wiring in a multilayerwiring structure at the same time.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional schematic view illustrating a configurationexample of a semiconductor device of a first example embodiment.

FIG. 2 is a conceptual diagram of current-voltage characteristics of arectifying element.

FIG. 3 is a conceptual diagram of current-voltage characteristicsbetween a first wiring and a second electrode of a three-terminalswitch.

FIG. 4 is a conceptual diagram of current-voltage characteristicsbetween a first wiring and a third electrode of a four-terminal switchwith rectifying elements.

FIG. 5 is another conceptual diagram of the current-voltagecharacteristics between the first wiring and the third electrode of thefour-terminal switch with rectifying elements.

FIG. 6(a) to (d) of FIG. 6 are cross-sectional schematic views for adescription of a method for producing the semiconductor device of thefirst example embodiment.

FIG. 7(a) to (d) of FIG. 7 are another cross-sectional schematic viewsfor a description of the method for producing the semiconductor deviceof the first example embodiment.

FIG. 8(a) to (d) of FIG. 8 are still another cross-sectional schematicviews for a description of the method for producing the semiconductordevice of the first example embodiment.

FIG. 9 is still another cross-sectional schematic view for a descriptionof the method for producing the semiconductor device of the firstexample embodiment.

FIG. 10 is a cross-sectional schematic view illustrating a configurationexample of a semiconductor device of a second example embodiment.

FIG. 11 is a cross-sectional schematic view illustrating a configurationexample of a semiconductor device of a third example embodiment.

FIG. 12 is a cross-sectional schematic view illustrating a configurationexample of a semiconductor device of a fourth example embodiment.

FIG. 13 is a cross-sectional schematic view illustrating a configurationexample of a semiconductor device of a fifth example embodiment.

FIG. 14 is a cross-sectional schematic view illustrating a configurationexample of a semiconductor device of a sixth example embodiment.

FIG. 15(a) to (c) of FIG. 15 are equivalent circuit diagrams ofmulti-terminal switches with rectifying elements and multi-terminalswitches of example embodiments.

FIG. 16(a) to (c) of FIG. 16 are equivalent circuit diagrams ofmulti-terminal switches with a rectifying element and multi-terminalswitches of example embodiments.

EXAMPLE EMBODIMENT

Preferred example embodiments of the present invention will be describedin detail with referent to the drawings. A semiconductor device of eachof the example embodiments includes a first switching element and asecond switching element disposed in a signal path of a logic circuit.The first switching element and the second switching element areprogrammable non-volatile switches. The first switching element ischaracterized by having a rectifying element and a variable resistanceelement, and the second switching element is characterized by having norectifying element and a variable resistance element. It is assumed thatthe first switching element and the second switching element are formedin the same wiring layer.

In FIGS. 15 and 16, equivalent circuit diagrams of semiconductor deviceseach of which includes a first switching element having a rectifyingelement(s) and a second switching element having no rectifying elementare illustrated. A lot of variations can be conceived by a combinationof the number of terminals in each switching element and whether or nota rectifying element is included in each switching element. (a) of FIG.15 is equivalent circuit diagrams of a four-terminal switch 122 withrectifying elements and a three-terminal switch 123 of an exampleembodiment. (b) of FIG. 15 is equivalent circuit diagrams of atwo-terminal switch 722 with a rectifying element and a two-terminalswitch 723 of an example embodiment. (c) of FIG. 15 is equivalentcircuit diagrams of a four-terminal switch 822 with rectifying elementsand a two-terminal switch 823 of an example embodiment. (a) of FIG. 16is equivalent circuit diagrams of a two-terminal switch 922 with arectifying element and a three-terminal switch 923 of an exampleembodiment. (b) and (c) of FIG. 16 are equivalent circuit diagrams of athree-terminal switch 1022 with a rectifying element and athree-terminal switch 1023 of an example embodiment and equivalentcircuit diagrams of a three-terminal switch 1122 with a rectifyingelement and a two-terminal switch 1123 of an example embodiment,respectively. Hereinafter, specific semiconductor devices of exampleembodiments and methods for producing the semiconductor devices will bedescribed.

First Example Embodiment

A semiconductor device according to a first example embodiment of thepresent invention and a method for producing the semiconductor devicewill be described. The present example embodiment is a semiconductordevice that has “a four-terminal switch with rectifying elements and athree-terminal switch” formed within a multilayer wiring layer. FIG. 1is a cross-sectional schematic view illustrating a configuration exampleof a semiconductor device of the first example embodiment. The presentexample embodiment is a semiconductor device that includes afour-terminal switch with rectifying elements and a three-terminalswitch within a multilayer wiring layer and the equivalent circuitdiagrams of which are illustrated in (a) of FIG. 15.

Configuration

The semiconductor device illustrated in FIG. 1 has a four-terminalswitch 122 with rectifying elements and a three-terminal switch 123within a multilayer wiring layer on a semiconductor substrate 101.

The multilayer wiring layer has an insulating stacked body in which, onthe semiconductor substrate 101, an interlayer insulating film 102, alow-k insulating film 103, an interlayer insulating film 104, a barrierinsulating film 107, a protection insulating film 114, an interlayerinsulating film 115, a low-k insulating film 116, an interlayerinsulating film 117, and a barrier insulating film 121 are stacked inthis sequence. The multilayer wiring layer has, in wiring grooves formedin the interlayer insulating film 104 and the low-k insulating film 103,first wirings 105 a and 105 b embedded with first barrier metals 106 aand 106 b in between, respectively. In addition, the multilayer wiringlayer has, in wiring grooves formed in the interlayer insulating film104 and the low-k insulating film 103, first wirings 105 c and 105 dembedded with first barrier metals 106 c and 106 d in between,respectively.

Further, the multilayer wiring layer has second wirings 118 a, 118 b,and 118 c embedded in wiring grooves formed in the interlayer insulatingfilm 117 and the low-k insulating film 116. Furthermore, vias 119 a, 119b, and 119 c are embedded in lower holes that are formed in theinterlayer insulating film 115, the protection insulating film 114, anda first hard mask film 112. Each of pairs of the second wiring 118 a andthe via 119 a, the second wiring 118 b and the via 119 b, and the secondwiring 118 c and the via 119 c are integrated into one body. Inaddition, the side surfaces and the bottom surfaces of pairs of thesecond wiring 118 a and the via 119 a, the second wiring 118 b and thevia 119 b, and the second wiring 118 c and the via 119 c are covered bysecond barrier metals 120 a, 120 b, and 120 c, respectively.

In an opening section formed in the barrier insulating film 107, on thefirst wirings 105 a and 105 b that serve as first electrodes, a portionof the interlayer insulating film 104 flanked by the first wirings 105 aand 105 b, the wall surface of the opening section in the barrierinsulating film 107, and the barrier insulating film 107, an ionconductive layer 109 a, a second electrode 110 a, a rectifying layer 108a, and a third electrode 111 are stacked in this sequence and thefour-terminal switch 122 with rectifying elements is thereby formed. Inaddition, on the third electrode 111, the first hard mask film 112 and asecond hard mask film 113 are formed. Further, the upper surface and theside face of a stacked body of the ion conductive layer 109 a, thesecond electrode 110 a, the rectifying layer 108 a, the third electrode111, the first hard mask film 112, and the second hard mask film 113 arecovered by the protection insulating film 114.

The multilayer wiring layer has, in another opening section formed inthe barrier insulating film 107, on the first wirings 105 c and 105 dthat serve as first electrodes, a portion of the interlayer insulatingfilm 104 flanked by the first wirings 105 c and 105 d, the wall surfaceof the another opening section in the barrier insulating film 107, andthe barrier insulating film 107, the three-terminal switch 123 formed inwhich an ion conductive layer 109 b, a second electrode 110 b, and arectifying layer 108 b are stacked in this sequence and the uppersurface and the side face of a stacked body of the ion conductive layer109 b and the second electrode 110 b covered by the protectioninsulating film 114.

Forming portions of the first wirings 105 a and 105 b into lowerelectrodes of the four-terminal switch 122 with rectifying elements andforming portions of the first wirings 105 c and 105 d into lowerelectrodes of the three-terminal switch 123, while simplifying thenumber of process steps, enable electrode resistance to be reduced. Onlygenerating a mask set of at least three PRs as additional process stepsto a regular copper damascene wiring process enables the four-terminalswitch 122 with rectifying elements and the three-terminal switch 123 tobe provided in the same wiring layer, which enables reduction in elementresistance and cost reduction to be achieved at the same time.

The four-terminal switch 122 with rectifying elements has the ionconductive layer 109 a in direct contact with the first wirings 105 aand 105 b in regions in the opening section formed in the barrierinsulating film 107. A metal constituting a portion of the ionconductive layer 109 a diffuses into the first wirings 105 a and 105 band thereby forms alloy layers.

The three-terminal switch 123 has the ion conductive layer 109 b indirect contact with the first wirings 105 c and 105 d in regions in theanother opening section formed in the barrier insulating film 107. Ametal constituting a portion of the ion conductive layer 109 b diffusesinto the first wirings 105 c and 105 d and thereby forms alloy layers.

The four-terminal switch 122 with rectifying elements has the rectifyinglayer 108 a on the second electrode 110 a, and the rectifying layer 108a is in contact with the third electrode 111 at the upper surface of therectifying layer 108 a. The third electrode 111 of the four-terminalswitch 122 with rectifying elements is electrically separated into tworegions by etching. On this occasion, the rectifying layer 108 a may beseparated into two regions as with the third electrode 111 or does nothave to be separated. On the third electrode 111, the first hard maskfilm 112 and the second hard mask film 113, which are separated as withthe third electrode 111, remain. The second hard mask film 113 does nothave to remain.

In the four-terminal switch 122 with rectifying elements, the vias 119 aand 119 b and the third electrode 111 are electrically connected to eachother with the second barrier metals 120 a and 120 b in between,respectively, on the third electrode 111.

The four-terminal switch 122 with rectifying elements is on/offcontrolled by applying voltage or flowing current between the secondelectrode 110 a and the first wiring 105 a or 105 b with the rectifyinglayer 108 a in between, such as being on/off controlled by use ofelectric field diffusion of metal ions supplied from a metal forming thefirst wirings 105 a and 105 b into the ion conductive layer 109 a. Onthis occasion, on-resistance is determined by current in the rectifyinglayer 108 a.

In the three-terminal switch 123, the via 119 c and the second electrode110 b are electrically connected to each other with the second barriermetal 120 c in between, on the second electrode 110 b. The rectifyinglayer 108 b may remain on the second electrode 110 b or may be removedwhen etching is performed in a production process of the three-terminalswitch 123. The three-terminal switch 123 is on/off controlled byapplying voltage or flowing current, such as being on/off controlled byuse of electric field diffusion of metal ions supplied from a metalforming the first wirings 105 c and 105 d into the ion conductive layer109 b.

The semiconductor substrate 101 is a substrate on which semiconductorelements are formed. For the semiconductor substrate 101, substrates,such as a silicon substrate, a single crystal substrate, a Silicon OnInsulator (SOI) substrate, a Thin Film Transistor (TFT) substrate, asubstrate for liquid crystal production and the like can be used.

The interlayer insulating film 102 is an insulating film that is formedon the semiconductor substrate 101. For the interlayer insulating film102, for example, a silicon oxide film, a SiOC film or the like can beused. The interlayer insulating film 102 may be a stack of a pluralityof insulating films.

For the low-k insulating film 103, a low dielectric constant film (forexample, a SiOCH film) or the like that has a lower relative dielectricconstant than a silicon oxide film is used. The low-k insulating film103 is an insulating film that is interposed between the interlayerinsulating films 102 and 104 and has a low dielectric constant. In thelow-k insulating film 103, wiring grooves for embedding the firstwirings 105 a, 105 b, 105 c, and 105 d are formed. In the wiring groovesin the low-k insulating film 103, the first wirings 105 a, 105 b, 105 c,and 105 d are embedded with the first barrier metals 106 a, 106 b, 106c, and 106 d in between, respectively.

The interlayer insulating film 104 is an insulating film that is formedon the low-k insulating film 103. For the interlayer insulating film104, for example, a silicon oxide film, a SiOC film or the like can beused. The interlayer insulating film 104 may be a stack of a pluralityof insulating films. In the interlayer insulating film 104, wiringgrooves for embedding the first wirings 105 a, 105 b, 105 c, and 105 dare formed. In the wiring grooves in the interlayer insulating film 104,the first wirings 105 a, 105 b, 105 c, and 105 d are embedded with thefirst barrier metals 106 a, 106 b, 106 c, and 106 d in between,respectively.

The first wirings 105 a and 105 b are wirings that are embedded in thewiring grooves formed in the interlayer insulating film 104 and thelow-k insulating film 103 with the first barrier metals 106 a and 106 bin between, respectively. The first wirings 105 a and 105 b also serveas the lower electrodes of the four-terminal switch 122 with rectifyingelements and are in direct contact with the ion conductive layer 109 a.The upper surface of the ion conductive layer 109 a is in direct contactwith the second electrode 110 a. As a metal constituting the firstwirings 105 a and 105 b, a metal that can diffuse and be ion-conductedin the ion conductive layer 109 a is used and, for example, copper orthe like can be used. The metal (for example, copper) constituting thefirst wirings 105 a and 105 b may be alloyed with aluminum.

The first wirings 105 c and 105 d are wirings that are embedded in thewiring grooves formed in the interlayer insulating film 104 and thelow-k insulating film 103 with the first barrier metals 106 c and 106 din between, respectively. The first wirings 105 c and 105 d also serveas the lower electrodes of the three-terminal switch 123 and are indirect contact with the ion conductive layer 109 b. The upper surface ofthe ion conductive layer 109 b is in direct contact with the secondelectrode 110 b. As a metal constituting the first wirings 105 c and 105d, a metal that can diffuse and be ion-conducted in the ion conductivelayer 109 b is used and, for example, copper or the like can be used.The metal (for example, copper) constituting the first wirings 105 c and105 d may be alloyed with aluminum.

The first barrier metals 106 a, 106 b, 106 c, and 106 d are conductivefilms having a barrier property. The first barrier metals 106 a, 106 b,106 c, and 106 d, in order to prevent the metal forming the firstwirings 105 a, 105 b, 105 c, and 105 d from diffusing into theinterlayer insulating film 104 and lower layers, covers the sidesurfaces and the bottom surfaces of the respective wirings. When thefirst wirings 105 a, 105 b, 105 c, and 105 d are constituted by metallicelements including copper as a main component, a refractory metal, anitride thereof or the like, such as tantalum, tantalum nitride,titanium nitride, and tungsten carbonitride, or a stacked film thereofcan be used for the first barrier metals 106 a, 106 b, 106 c, and 106 d.

The barrier insulating film 107 is formed on the interlayer insulatingfilm 104 including the first wirings 105 a, 105 b, 105 c, and 105 d.This configuration enables the barrier insulating film 107 to have rolesof preventing the metal (for example, copper) forming the first wirings105 a, 105 b, 105 c, and 105 d from being oxidized, preventing the metalforming the first wirings 105 a, 105 b, 105 c, and 105 d from diffusinginto the interlayer insulating film 115, and working as an etching stoplayer at the time of processing the third electrode 111, the rectifyinglayers 108 a and 108 b, the second electrodes 110 a and 110 b, and theion conductive layers 109 a and 109 b. For the barrier insulating film107, for example, a SiC film, a silicon carbonitride film, a siliconnitride film, a stacked structure thereof or the like can be used. Thebarrier insulating film 107 is preferably made of the same material asthe protection insulating film 114 and the first hard mask film 112.

The ion conductive layers 109 a and 109 b are films the resistance ofwhich changes. For the ion conductive layers 109 a and 109 b, a materialthe resistance of which changes due to action (diffusion, ionicconduction, or the like) of metal ions generated from the metal formingthe first wirings 105 a, 105 b, 105 c, and 105 d (lower electrodes) canbe used. When resistance change in association with switching to anon-state is achieved through deposition of a metal by reduction of metalions, a film capable of conducting ions is used for the ion conductivelayers 109 a and 109 b.

The ion conductive layers 109 a and 109 b are respectively constitutedby ion conductive layers that are made of a metal oxide and are incontact with the first wirings 105 a, 105 b, 105 c, and 105 d and ionconductive layers that are made of a polymer and are in contact with thesecond electrodes 110 a and 110 b.

The ion conductive layer made of a polymer in each of the ion conductivelayers 109 a and 109 b is formed using a plasma-enhanced chemical vapordeposition (plasma-enhanced CVD) method. Raw material of cyclicorganosiloxane and helium, which is a carrier gas, are flowed into areaction chamber, and, when the supply of both the cyclic organosiloxaneand helium has stabilized and pressure in the reaction chamber hasbecome constant, application of Radio Frequency (RF) electric power isstarted. The amount of supply of the raw material is set at 10 to 200sccm, and 500 sccm helium is supplied via a raw material vaporizer.

The ion conductive layer made of a metal oxide in each of the ionconductive layers 109 a and 109 b has a plurality of roles. One role isto prevent the metal forming the first wirings 105 a, 105 b, 105 c, and105 d from diffusing into the ion conductive layer made of a polymer dueto application of heat and plasma during deposition of the ionconductive layer made of a polymer. Another role is to prevent the firstwirings 105 a, 105 b, 105 c, and 105 d from being oxidized and becomingeasily accelerated to diffuse into the ion conductive layer made of apolymer. A metal, such as zirconium, hafnium, aluminum and titanium,that forms the ion conductive layer made of a metal oxide, after filmformation of the metal that constitutes the ion conductive layer made ofa metal oxide, is exposed to an oxygen atmosphere under reduced pressurein a film forming chamber for the ion conductive layer made of a polymerand becomes zirconium oxide, hafnium oxide, aluminum oxide, or titaniumoxide, thereby becoming a portion of each of the ion conductive layers109 a and 109 b. An optimum thickness of a metal film that forms the ionconductive layer made of a metal oxide is 0.5 to 1 nm. The metal filmthat is used for forming the ion conductive layer made of a metal oxidemay form a stack or a single layer. Film formation of the metal filmthat is used for forming the ion conductive layer made of a metal oxideis preferably performed by sputtering. Metal atoms or ions havingacquired energy through sputtering plunge and diffuse into the firstwirings 105 a, 105 b, 105 c, and 105 d and form alloy layers.

The ion conductive layer 109 a is formed on the first wirings 105 a and105 b, a portion of the interlayer insulating film 104 flanked by thefirst wirings 105 a and 105 b, tapered surfaces formed in the openingsection in the barrier insulating film 107, and the barrier insulatingfilm 107.

The ion conductive layer 109 b is formed on the first wirings 105 c and105 d, a portion of the interlayer insulating film 104 flanked by thefirst wirings 105 c and 105 d, tapered surfaces formed in the anotheropening section in the barrier insulating film 107, and the barrierinsulating film 107.

The second electrodes 110 a and 110 b are upper electrodes of thefour-terminal switch 122 with rectifying elements and the three-terminalswitch 123 and are in direct contact with the ion conductive layers 109a and 109 b, respectively.

For the second electrodes 110 a and 110 b, a ruthenium alloy containingtitanium, tantalum, zirconium, hafnium, aluminum or the like is used.Ruthenium is a metal that is harder to ionize than the metal forming thefirst wirings 105 a, 105 b, 105 c, and 105 d and is hard to diffuse andbe ion-conducted in the ion conductive layers 109 a and 109 b. Titanium,tantalum, zirconium, hafnium, or aluminum that is added to a rutheniumalloy has a good adhesiveness with the metal forming the first wirings105 a, 105 b, 105 c, and 105 d. As a first metal that constitutes thesecond electrodes 110 a and 110 b and is added to ruthenium, it ispreferable to select a metal that has a standard Gibbs energy offormation of a process of generating metal ions from the metal(oxidation process) larger than ruthenium in the negative direction.Because of having a standard Gibbs energy of formation of a process ofgenerating metal ions from a metal (oxidation process) larger thanruthenium in the negative direction and being more likely tospontaneously react chemically than ruthenium, titanium, tantalum,zirconium, hafnium, aluminum and the like are highly reactive. For thisreason, in the ruthenium alloy that forms the second electrodes 110 aand 110 b, alloying titanium, tantalum, zirconium, hafnium, aluminum orthe like with ruthenium improves adhesiveness thereof with metalcross-links formed by the metal forming the first wirings 105 a, 105 b,105 c, and 105 d.

On the other hand, an additive metal itself like titanium, tantalum,zirconium, hafnium, aluminum or the like, not alloyed with ruthenium,becomes too highly reactive, which causes a transition to an “OFF” statenot to occur. While a transition from an “ON” state to an “OFF” stateproceeds through oxidation reaction (dissolution reaction) of metalcross-links, when a metal constituting the second electrodes 110 a and110 b has a standard Gibbs energy of formation of a process ofgenerating metal ions from the metal (oxidation process) larger, in thenegative direction, than the metal forming the first wirings 105 a, 105b, 105 c, and 105 d, the oxidation reaction of the metal constitutingthe second electrodes 110 a and 110 b proceeds faster than the oxidationreaction of metal cross-links formed by the metal forming the firstwirings 105 a, 105 b, 105 c, and 105 d, which causes a transition to the“OFF” state not to occur.

For this reason, a metal material that is used to form the metalconstituting the second electrodes 110 a and 110 b is required to bealloyed with ruthenium that has a standard Gibbs energy of formation ofa process of generating metal ions from the metal (oxidation process)smaller than copper in the negative direction.

Further, when copper, which is a component of metal cross-links, mixeswith the metal constituting the second electrodes 110 a and 110 b, aneffect of adding a metal having a large standard Gibbs energy offormation in the negative direction is reduced. For this reason, amaterial having a barrier property against copper and copper ions ispreferable as a metal added to ruthenium. Such materials include, forexample, tantalum and titanium. On the other hand, it has been revealedthat, the larger the amount of additive metal is, the more stable an“ON” state becomes, and even an addition of only 5 atm % metal improvesthe stability. In particular, a case of using titanium as an additivemetal excels in transition to an-off state and stability of an on-state,and it is particularly preferable that an alloy of ruthenium andtitanium be used as the metal constituting the second electrodes 110 aand 110 b and a content of titanium be set at a value within a rangefrom 20 atm % to 30 atm %. A content of ruthenium in the ruthenium alloyis preferably set at a value of 60 atm % or higher and 90 atm % orlower.

For forming a ruthenium alloy, it is preferable to use a sputteringmethod. When an alloy is film-formed using a sputtering method, thesputtering methods include a method of using a target made of an alloyof ruthenium and the first metal, a co-sputtering method of sputtering aruthenium target and a first metal target in the same chamber at thesame time, and an intermixing method in which a thin film of the firstmetal is formed in advance, ruthenium is film-formed on the thin film bya sputtering method, and the first metal and the ruthenium are alloyedwith energy of colliding atoms. Use of the co-sputtering method and theintermixing method enables composition of an alloy to be altered. Whenthe intermixing method is employed, it is preferable that, afterruthenium film formation has been finished, heat treatment at atemperature of 400° C. or lower be performed for “planarization” of themixed state of metals.

The second electrodes 110 a and 110 b preferably have a two-layerstructure. When the sides of the second electrodes 110 a and 110 b incontact with the ion conductive layers 109 a and 109 b are made of aruthenium alloy, the sides of the second electrodes 110 a and 110 b incontact with the rectifying layers 108 a and 108 b serve as lowerelectrodes of the rectifying elements. As a metal species, a metalnitride, such as titanium nitride and tantalum nitride, that isdifficult to be oxidized, easy to process, and the work function ofwhich is adjustable by adjusting composition thereof can be used.

Titanium and tantalum may also be used as long as being able to inhibitoxidation at boundary faces of the second electrodes 110 a and 110 bwith the rectifying layers 108 a and 108 b. Titanium nitride, tantalumnitride, titanium, or tantalum is film-formed on the ruthenium alloylayer by a sputtering method in a continuous vacuum process. Whentitanium or tantalum is nitrided, the nitride is film-formed byintroducing nitrogen into a chamber and using a reactive sputteringmethod.

The rectifying layers 108 a and 108 b are layers that have a bipolarrectification effect and have a characteristic in which currentincreases in a non-linear manner with respect to applied voltage. APoole-Frenkel type insulating film, a Schottky type insulating film, athreshold switching type volatile variable-resistance film, or the likecan be used as the rectifying layers 108 a and 108 b. For example, afilm containing any of titanium oxide, tungsten oxide, molybdenum oxide,hafnium oxide, aluminum oxide, zirconium oxide, yttrium oxide, manganeseoxide, niobium oxide, silicon nitride, silicon carbonitride, siliconoxide and amorphous silicon can be used as the rectifying layers 108 aand 108 b. In particular, constituting a stack by stacking amorphoussilicon, silicon nitride, and amorphous silicon in this sequence enablesexcellent non-linearity to be generated. By, by means of interposing asilicon nitride film between amorphous silicon films, causingcomposition of a portion of the silicon nitride film to be brought to astate in which nitrogen is deficient from the stoichiometric ratio andthereby reducing differences in barrier heights with the secondelectrodes 110 a and 110 b and the third electrode 111, it is possibleto facilitate tunneling current to flow to the silicon nitride at thetime of high voltage application. As a result, a non-linear currentchange is generated.

The third electrode 111 is a metal that serves as upper electrodes ofthe rectifying elements, and, for example, tantalum, titanium, tungsten,a nitride thereof, or the like can be used for the third electrode 111.In order to make current-voltage characteristics of the rectifyingelements symmetrical in both positive and negative sides, it ispreferable to use the same material as those of the second electrodes110 a and 110 b for the third electrode 111. The third electrode 111also has a function as an etching stop layer when the vias 119 a and 119b are electrically connected onto the second electrode 110 a. Thus, itis preferable that the third electrode 111 have a low etching rate forplasma of a fluorocarbon-based gas that is used in etching of theinterlayer insulating film 115. For forming the third electrode 111, itis preferable to use a sputtering method. When a metal nitride isfilm-formed using a sputtering method, it is preferable to use areactive sputtering method in which a metal target is vaporized usingplasma of a gas mixture of nitrogen and argon. A metal vaporized fromthe metal target reacts with nitrogen and forms a metal nitride, whichis film-formed on a substrate.

The third electrode 111 is present only on the four-terminal switch 122with rectifying elements in which rectifying elements are formed andseparated into two regions on the four-terminal switch 122 withrectifying elements. As a result, two rectifying elements are arrangedon the four-terminal switch 122 with rectifying elements independentlyof each other.

The first hard mask film 112 is a film that serves as a hard mask filmand a passivation film when the third electrode 111, the secondelectrodes 110 a and 110 b, the rectifying layers 108 a and 108 b, andthe ion conductive layers 109 a and 109 b are etched. For the first hardmask film 112, for example, a silicon nitride film, a silicon oxide filmor the like, or a stack thereof can be used. The first hard mask film112 preferably includes the same material as the protection insulatingfilm 114 and the barrier insulating film 107.

The second hard mask film 113 is a film that serves as a hard mask filmwhen the third electrode 111, the second electrodes 110 a and 110 b, therectifying layers 108 a and 108 b, and the ion conductive layers 109 aand 109 b are etched. For the second hard mask film 113, for example, asilicon nitride film, a silicon oxide film or the like, or a stackthereof can be used.

Based on a shape of the second hard mask film 113, the four-terminalswitch 122 with rectifying elements and the three-terminal switch 123are formed differently from each other. On the barrier insulating film107 of both the four-terminal switch 122 with rectifying elements andthe three-terminal switch 123, the ion conductive layers 109 a and 109b, the second electrodes 110 a and 110 b, the rectifying layers 108 aand 108 b, the third electrode 111, the first hard mask film 112, andthe second hard mask film 113 are film-formed. Subsequently, in a mannerin which a shape of the second hard mask film 113, formed through tworounds of patterning and etching, is transferred onto the four-terminalswitch 122 with rectifying elements, two rectifying elements are formedseparated from each other on the second electrode 110 a in one round ofetching.

That is, a stacked structure for the four-terminal switch 122 withrectifying elements is film-formed once on the whole wafer, and, on anelement portion to which the three-terminal switch 123 is to be formed,patterning for forming a rectifying element portion in the four-terminalswitch 122 with rectifying elements is configured not to be performed (aresist is configured not to be left). This configuration causesthickness of a portion of the second hard mask film 113 on thethree-terminal switch 123 to be reduced. Subsequently, performingetching enables a portion of the third electrode 111 on thethree-terminal switch 123 to be removed. That is, an area on thethree-terminal switch 123 is brought into the same condition as an areaon the four-terminal switch 122 with rectifying elements except an areaunder which the rectifying elements are formed. The rectifying layer 108b may or does not have to remain on the second electrode 110 a of thethree-terminal switch 123. In addition, the first hard mask film 112 andthe second hard mask film 113 do not remain on the three-terminal switch123.

The protection insulating film 114 is an insulating film that hasfunctions of preventing the four-terminal switch 122 with rectifyingelements and the three-terminal switch 123 from being damaged andfurther preventing desorption of oxygen from the ion conductive layers109 a and 109 b. For the protection insulating film 114, for example, asilicon nitride film, a silicon carbonitride film or the like can beused. The protection insulating film 114 is preferably made of the samematerial as the first hard mask film 112 and the barrier insulating film107. In the case of being made of the same material, the protectioninsulating film 114 is integrated into one body with the barrierinsulating film 107 and the first hard mask film 112 and adhesiveness ofboundary faces thereamong is thereby improved, which enables thefour-terminal switch 122 with rectifying elements and the three-terminalswitch 123 to be protected more securely.

The interlayer insulating film 115 is an insulating film that is formedon the protection insulating film 114. For the interlayer insulatingfilm 115, for example, a silicon oxide film, a SiOC film or the like canbe used. The interlayer insulating film 115 may be a stack of aplurality of insulating films. The interlayer insulating film 115 may bemade of the same material as the interlayer insulating film 117. In theinterlayer insulating film 115, lower holes for embedding the vias 119a, 119 b, and 119 c are formed, and, in the lower holes, the vias 119 a,119 b, and 119 c are embedded with the second barrier metals 120 a, 120b, and 120 c in between, respectively.

For the low-k insulating film 116, a low dielectric constant film (forexample, a SiOCH film) or the like that has a lower relative dielectricconstant than a silicon oxide film is used. The low-k insulating film116 is an insulating film that is interposed between the interlayerinsulating films 115 and 117 and has a low dielectric constant. In thelow-k insulating film 116, wiring grooves for embedding the secondwirings 118 a, 118 b, and 118 c are formed. In the wiring grooves in thelow-k insulating film 116, the second wirings 118 a, 118 b, and 118 care embedded with the second barrier metals 120 a, 120 b, and 120 c inbetween, respectively.

The interlayer insulating film 117 is an insulating film that is formedon the low-k insulating film 116. For the interlayer insulating film117, for example, a silicon oxide film, a SiOC film, a low dielectricconstant film (for example, a SiOCH film) that has a lower relativedielectric constant than a silicon oxide film, or the like can be used.The interlayer insulating film 117 may be a stack of a plurality ofinsulating films. The interlayer insulating film 117 may be made of thesame material as the interlayer insulating film 115. In the interlayerinsulating film 117, wiring grooves for embedding the second wirings 118a, 118 b, and 118 c are formed. In the wiring grooves in the interlayerinsulating film 117, the second wirings 118 a, 118 b, and 118 c areembedded with the second barrier metals 120 a, 120 b, and 120 c inbetween, respectively.

The second wirings 118 a, 118 b, and 118 c are wirings that are embeddedin the wiring grooves formed in the interlayer insulating film 117 andthe low-k insulating film 116 with the second barrier metals 120 a, 120b, and 120 c in between, respectively. The second wirings 118 a, 118 b,and 118 c are integrated into one body with the vias 119 a, 119 b, and119 c, respectively.

The vias 119 a and 119 b are embedded in the lower holes formed in theinterlayer insulating film 115, the protection insulating film 114, thefirst hard mask film 112, and the second hard mask film 113 with thesecond barrier metals 120 a and 120 b in between, respectively. The via119 c is embedded in the lower hole formed in the interlayer insulatingfilm 115 and the protection insulating film 114 with the second barriermetal 120 c in between.

The vias 119 a and 119 b are electrically connected to the thirdelectrode 111 with the second barrier metals 120 a and 120 b in between,respectively. The via 119 c is electrically connected to the secondelectrode 110 b with the second barrier metal 120 c in between. For thesecond wirings 118 a, 118 b, and 118 c and the vias 119 a, 119 b, and119 c, for example, copper can be used.

The second barrier metals 120 a, 120 b, and 120 c are conductive filmsthat cover the side surfaces and the bottom surfaces of the secondwirings 118 a, 118 b, and 118 c and the vias 119 a, 119 b, and 119 c,respectively and have a barrier property. The second barrier metals 120a, 120 b, and 120 c prevent a metal forming the second wirings 118 a,118 b, and 118 c (including the vias 119 a, 119 b, and 119 c) fromdiffusing into the interlayer insulating films 115 and 117 and lowerlayers.

For example, when the second wirings 118 a, 118 b, and 118 c and thevias 119 a, 119 b, and 119 c are constituted by metallic elementsincluding copper as a main component, a refractory metal, a nitridethereof or the like, such as tantalum, tantalum nitride, titaniumnitride, and tungsten carbonitride, or a stack thereof can be used forthe second barrier metals 120 a, 120 b, and 120 c.

The barrier insulating film 121 is an insulating film that is formed onthe interlayer insulating film 117 including the second wirings 118 a,118 b, and 118 c. The barrier insulating film 121 has roles ofpreventing the metal (for example, copper) forming the second wirings118 a, 118 b, and 118 c from being oxidized and preventing the metalforming the second wirings 118 a, 118 b, and 118 c from diffusing intoupper layers. For the barrier insulating film 121, for example, asilicon carbonitride film, a silicon nitride film, a stacked structurethereof or the like can be used.

Embodiment Mode 1

An advantageous effect of “a three-terminal switch with rectifyingelements and a three-terminal switch formed within a multilayer wiringlayer” described in the first example embodiment described above will bedescribed in accordance with FIGS. 2 to 5. In addition, an elementconfiguration will be described in accordance with the terminologyillustrated in FIG. 1.

In FIG. 2, a conceptual diagram of current-voltage characteristics of arectifying element is illustrated. When voltage is applied between thesecond electrode 110 a and the third electrode 111 of the four-terminalswitch 122 with rectifying elements, the rectifying element exhibitscurrent-voltage characteristics through the rectifying layer 108 a thatare non-linear and symmetrical in the positive and negative sides. Whilea high resistance is indicated in a low-voltage region, the currentincreases exponentially as the applied voltage increases. Resistancechange is not retained in a non-volatile state, and, when voltageapplication is stopped, a low-resistance state is immediately releasedin a volatile manner.

In FIG. 3, a conceptual diagram of current-voltage characteristicsbetween a first wiring and the second electrode of the three-terminalswitch 123. When the second electrode 110 b is grounded and a positivevoltage is applied to the first wiring 105 c, a metal constituting thefirst wiring 105 c is ionized through an electrochemical reaction andmetal ions are implanted into the ion conductive layer 109 b. Theimplanted metal ions migrate to the second electrode 110 b side and,receiving electrons, deposit in the ion conductive layer 109 b as metalcross-links. When the second electrode 110 b and the first wiring 105 care connected by the metal cross-links, the three-terminal switch 123transitions to a low-resistance state (on-state) at V3 in FIG. 3. On theother hand, when a negative voltage is applied to the first wiring 105c, the metal cross-links are ionized into metal ions through adissolution reaction and the metal ions are collected by the firstwiring 105 c, as a result of which the three-terminal switch 123transitions to a high-resistance state (off-state) at −V3 in FIG. 3.Resistance change in the three-terminal switch 123 is retained in anon-volatile manner even after the applied voltage is cut off. When thethree-terminal switch 123 transitions to the low-resistance state,current limitation is applied by a transistor connected in series and aresistance value in the low-resistance state is thereby determined. Thatis, thickness of the metal cross-links can be controlled by the currentlimitation by the transistor. Between the first wiring 105 d and thesecond electrode 110 b of the three-terminal switch 123, current-voltagecharacteristics similar to the current-voltage characteristics describedabove are also exhibited.

In FIGS. 4 and 5, conceptual diagrams of current-voltage characteristicsbetween the first wiring 105 a and the region of the third electrode 111in contact with the via 119 b of the four-terminal switch 122 withrectifying elements are illustrated. While non-volatile switching in thefour-terminal switch 122 with rectifying elements exhibits the samecurrent-voltage characteristics as the current-voltage characteristics(FIG. 3) between the first wiring 105 c and the second electrode 110 bof the three-terminal switch 123, current limitation is performed by therectifying layer 108 a. For this reason, the current-voltagecharacteristics of the four-terminal switch 122 with rectifying elementsexhibit current-voltage characteristics into which the current-voltagecharacteristics in FIGS. 2 and 3 are merged. In FIG. 4, thecurrent-voltage characteristics in FIGS. 2 and 3 are illustrated in asuperimposed manner.

When the region of the third electrode 111 in contact with the via 119 bis grounded and positive voltage is applied to the first wiring 105 a,the four-terminal switch 122 with rectifying elements exhibitscurrent-voltage characteristics of a high-resistance rectifying elementuntil the voltage reaches V2 at which the current-voltagecharacteristics in FIGS. 2 and 3 cross each other. For this reason, ahigh-resistance state is maintained at V1 that is a readout voltage inan off-state, which enables sneak current to be inhibited from flowing.While the four-terminal switch 122 with rectifying elements exhibits thecurrent-voltage characteristics of the three-terminal switch 123 in ahigh-resistance state within a range of voltage from V2 to V3 at whichthe ion conductive layer 109 a between the first wiring 105 a and thesecond electrode 110 a transitions to a low-resistance state, thefour-terminal switch 122 with rectifying elements exhibits thecurrent-voltage characteristics of a rectifying element after the ionconductive layer 109 a between the first wiring 105 a and the secondelectrode 110 a has transitioned to a low-resistance state. On the otherhand, when negative voltage is applied to the first wiring 105 a, whilethe four-terminal switch 122 with rectifying elements first exhibits thecurrent-voltage characteristics of a rectifying element until thevoltage reaches −V3 at which the ion conductive layer 109 a between thefirst wiring 105 a and the second electrode 110 a transitions to ahigh-resistance state and, subsequently, exhibits the current-voltagecharacteristics of the three-terminal switch 123 within a range ofvoltage from −V3 to −V2 at which the current-voltage characteristics inFIGS. 2 and 3 cross each other, the four-terminal switch 122 withrectifying elements exhibits the current-voltage characteristics of ahigh-resistance rectifying element within a range of voltage from −V2 to0 V.

In FIG. 5, current-voltage characteristics between the first wiring 105a and the region of the third electrode 111 in contact with the via 119b of the four-terminal switch 122 with rectifying elements areillustrated. Between the first wiring 105 b and the region of the thirdelectrode 111 in contact with the via 119 a of the four-terminal switch122 with rectifying elements, current-voltage characteristics similar tothe current-voltage characteristics described above are also exhibited.

Embodiment Mode 2

Next, a method for producing a semiconductor device of the presentexample embodiment will be described with reference to FIGS. 6 to 9.Specifically, a method for producing a semiconductor device that has “afour-terminal switch with rectifying elements and a three-terminalswitch formed within a multilayer wiring layer” will be described. Inparticular, production steps in which switching elements employing aconfiguration of “a four-terminal switch with rectifying elements and athree-terminal switch” are formed within a multilayer wiring layer willbe described.

Step 1

On a semiconductor substrate 601 (for example, a substrate on whichsemiconductor devices are formed), an interlayer insulating film 602(for example, a silicon oxide film having a thickness of 500 nm) isdeposited, and, subsequently, a low dielectric constant film (forexample, a SiOCH film having a thickness of 150 nm) that has a lowrelative dielectric constant is deposited on the interlayer insulatingfilm 602 as a low-k insulating film 603. Subsequently, a silicon oxidefilm (for example, a silicon oxide film having a thickness of 100 nm) isdeposited on the low-k insulating film 603 as an interlayer insulatingfilm 604. Subsequently, using a lithography method (includingphotoresist formation, dry etching, and photoresist removal), wiringgrooves are formed in the interlayer insulating film 604 and the low-kinsulating film 603. Subsequently, in the wiring grooves, first wirings605 a, 605 b, 605 c, and 605 d (for example, copper) are embedded withfirst barrier metals 606 a, 606 b, 606 c, and 606 d (for example,tantalum having a film thickness of 5 nm and tantalum nitride having afilm thickness of 5 nm) in between, respectively ((a) of FIG. 6).

The interlayer insulating films 602 and 604 can be formed by aplasma-enhanced CVD method. The first wirings 605 a, 605 b, 605 c, and605 d can be formed by, for example, forming the first wirings 605 a,605 b, 605 c, and 605 d (for example, a stacked film of tantalum nitrideand tantalum) by a Physical Vapor Deposition (PVD) method, buryingcopper in the wiring grooves by an electrolytic plating method afterforming copper seeds by the PVD method, and, after heat treatment at atemperature of 150° C. or higher, removing surplus copper other thancopper in the wiring grooves by a Chemical Mechanical Polishing (CMP)method. As such a series of forming method of copper wirings, generalmethods in the technological field can be used. As used herein, the CMPmethod is a method for planarizing unevenness of a wafer surfacegenerated in a multilayer wiring formation process by, flowing apolishing solution on the wafer surface, polishing the wafer surfacewith the wafer surface in contact with a rotated polishing pad. The CMPmethod is used for forming an embedded wiring (damascene wiring) bypolishing surplus copper embedded in a groove or performingplanarization by polishing an interlayer insulating film.

Step 2

Next, as illustrated in (b) of FIG. 6, on the interlayer insulating film604 including the first wirings 605 a, 605 b, 605 c, and 605 d, abarrier insulating film 607 (for example, a silicon nitride film or asilicon carbonitride film having a thickness of 30 nm) is formed. Thebarrier insulating film 607 can be formed using the plasma-enhanced CVDmethod. Thickness of the barrier insulating film 607 is preferablyapproximately 10 nm to 50 nm.

Step 3

Next, on the barrier insulating film 607, a hard mask film 624 (forexample, a silicon oxide film having a thickness of 40 nm) is formed. Onthis occasion, the hard mask film 624 is preferably made of a materialdifferent from the material of the barrier insulating film 607 in termsof keeping an etching selectivity in dry etching processing at a highlevel and may be an insulating film or a conductive film. For the hardmask film 624, for example, silicon oxide, silicon nitride, titaniumnitride, titanium, tantalum, tantalum nitride or the like can be usedand a stacked body of a silicon nitride film and a silicon oxide filmcan also be used. Openings are patterned on the hard mask film 624 byuse of a photoresist (not illustrated), opening patterns are formed onthe hard mask film 624 by performing dry etching by use of thephotoresist as a mask, and, subsequently, the photoresist is stripped byoxygen plasma ashing or the like ((c) of FIG. 6). On this occasion, thedry etching does not always have to be stopped at the upper surface ofthe barrier insulating film 607 and may reach the inside of the barrierinsulating film 607.

Step 4

Openings are formed on the barrier insulating film 607 by etching back(dry etching) portions of the barrier insulating film 607 exposed fromthe openings of the hard mask film 624 by use of the hard mask film 624as a mask, and the first wirings 605 a, 605 b, 605 c, and 605 d arethereby exposed from the openings of the barrier insulating film 607((d) of FIG. 6). Subsequently, by exposing the barrier insulating film607 and the openings thereof to plasma using a gas mixture of nitrogenand argon, copper oxide formed on exposed surfaces of the first wirings605 a, 605 b, 605 c, and 605 d are removed and, therewith, etchingby-products and the like generated at the time of the etch-back areremoved. In the etch-back of the barrier insulating film 607, use ofreactive dry etching enables wall surfaces of the openings of thebarrier insulating film 607 to be formed into tapered surfaces. In thereactive dry etching, a gas containing fluorocarbon can be used as anetching gas. Although the hard mask film 624 is preferably removedcompletely in the etch-back, the hard mask film 624 may be leftunremoved when the hard mask film 624 is made of an insulating material.In addition, a shape of each opening of the barrier insulating film 607may be configured to be a circle, the diameter of which is 30 nm to 500nm.

Step 5

On the barrier insulating film 607 including the first wirings 605 a,605 b, 605 c, and 605 d, an ion conductive layer 609 is formed. First, azirconium film having a thickness of 1 nm is deposited by a sputteringmethod. The zirconium is oxidized when an ion conductive layer made of apolymer is film-formed and forms a portion of the ion conductive layer609. On this occasion, the zirconium diffuses into portions of the firstwirings 605 a, 605 b, 605 c, and 605 d that are in contact with the ionconductive layer 609, and alloy layers are spontaneously formed.Further, performing annealing under a vacuum environment at atemperature of 350° C. enables thickness of the alloy layers to beincreased. The annealing is preferably performed for approximately 2minutes. Further, a SiOCH-based polymer film containing silicon, oxygen,carbon, and hydrogen is formed as an ion conductive layer made of apolymer by a plasma-enhanced CVD method. Raw material of cyclicorganosiloxane and helium, which is a carrier gas, are flowed into areaction chamber, and, when the supply of both the cyclic organosiloxaneand helium has stabilized and pressure in the reaction chamber hasbecome constant, application of RF electric power is started. The amountof supply of the raw material is set at 10 to 200 sccm, and 500 sccmhelium is supplied via a raw material vaporizer and another 500 sccmhelium is supplied directly to the reaction chamber via a differentline. Since moisture or the like adhere to the openings of the barrierinsulating film 607 through air exposure, it is preferable to, beforethe ion conductive layer made of a polymer is deposited, performdegassing by performing heat treatment at a temperature of approximately250° C. to 350° C. under reduced pressure.

On the ion conductive layer 609, a second electrode 610 having a stackedstructure of an upper layer and a lower layer is formed. First, as thelower layer of the second electrode 610, an “alloy of ruthenium andtitanium” is formed in a film thickness of 10 nm by a co-sputteringmethod. On this occasion, a ruthenium target and a titanium target arepresent in the same chamber, and sputtering both targets at the sametime causes an alloy film to deposit. On this occasion, by settingapplied power to the ruthenium target and the titanium target at 150 Wand 50 W, respectively, a content of ruthenium in the “alloy ofruthenium and titanium” is set at 75 atm %. The ruthenium alloy servesas an upper electrode of the three-terminal switch. Further, as theupper layer of the second electrode 610, titanium nitride is formed onthe ruthenium alloy in a film thickness of 5 nm to 10 nm by a reactivesputtering method. On this occasion, the sputtering is performed settingapplied power to a titanium target at 500 W to 1 kW and introducing anitrogen gas and an argon gas into a chamber. On this occasion, bysetting a ratio between a flow rate of nitrogen and a flow rate of argonat 1:1, a ratio of titanium to titanium nitride is set at 70 atm %.

On the second electrode 610, amorphous silicon, silicon nitride, andamorphous silicon are film-formed in this sequence as a rectifying layer608 by the plasma-enhanced CVD method. Thickness of each film ispreferably 5 nm or thinner. For example, amorphous silicon and siliconnitride are film-formed in a thickness of 2 nm and a thickness of 1 nm,respectively. The film formation is performed in a continuous manner byswitching gases to be introduced while plasma is ignited. Adjustment offlow rates of SiH₄ gas and nitrogen gas enables composition of siliconnitride to be controlled. On this occasion, setting a ratio between theflow rate of the SiH₄ gas and the flow rate of the nitrogen gas at 4:1enables silicon nitride having composition close to the stoichiometricratio to be obtained.

On the rectifying layer 608, titanium nitride is formed in a filmthickness of 15 nm to 25 nm as a third electrode 611 by the reactivesputtering method. On this occasion, the sputtering is performed settingapplied power to a titanium target at 500 W to 1 kW and introducing anitrogen gas and an argon gas into a chamber. On this occasion, bysetting a ratio between a flow rate of nitrogen and a flow rate of argonat 1:1, a ratio of titanium to titanium nitride is set at 70 atm % ((a)of FIG. 7).

Step 6

On the third electrode 611, a first hard mask film 612 (for example, asilicon nitride film or a silicon carbonitride film having a thicknessof 30 nm) and a second hard mask film 613 (for example, a silicon oxidefilm having a thickness of 100 nm) are stacked in this sequence ((b) ofFIG. 7). The first hard mask film 612 and the second hard mask film 613can be film-formed using the plasma-enhanced CVD method. The first hardmask film 612 and the second hard mask film 613 can be formed using ageneral plasma-enhanced CVD method in the technical field. In addition,the first hard mask film 612 and the second hard mask film 613 arepreferably different types of films, and, for example, the first hardmask film 612 and the second hard mask film 613 can be a silicon nitridefilm and a silicon oxide film, respectively. On this occasion, the firsthard mask film 612 is preferably made of the same material as that of aprotection insulating film 614 and a barrier insulating film 607, whichwill be described later. In addition, while the first hard mask film 612can be formed by the plasma-enhanced CVD method, it is preferable to usea high-density silicon nitride film or the like by, for example,transforming a SiH₄/N₂ gas mixture into a high-density plasma.

Step 7

On the second hard mask film 613, photoresists 625 for patterningrectifying element portions of the four-terminal switch with rectifyingelements are formed by a lithography method ((c) of FIG. 7). On thisoccasion, on a portion of the second hard mask film 613 on thethree-terminal switch, in which no rectifying element is formed, thepatterning is not performed and the photoresist is removed at the timeof development and is not left.

Step 8

Using the photoresists 625 as masks, a portion of the second hard maskfilm 613 is dry-etched, and, subsequently, the photoresists are removedusing oxygen plasma ashing and organic stripping ((d) of FIG. 7). Filmthickness in an area where the photoresists 625 were not formed isreduced by etching, and film thickness in areas where the photoresists625 were formed are not reduced. Etched film thickness is preferablyapproximately 30 nm to 70 nm. Specifically, etched film thickness,remaining film thickness in areas of the second hard mask film 613 wherethe photoresists 625 were formed, and remaining film thickness in anarea of the second hard mask film 613 where the photoresists 625 werenot formed are preferably approximately 60 nm, 100 nm, and 40 nm,respectively.

Step 9

On the processed second hard mask film 613, photoresists 626 forpatterning switching element portions of the four-terminal switch withrectifying elements and the three-terminal switch are formed by thelithography method ((a) of FIG. 8).

Step 10

Using the photoresists 626 as masks, a remaining portion of the secondhard mask film 613 is dry-etched, and, subsequently, the photoresistsare removed using oxygen plasma ashing and organic stripping ((b) ofFIG. 8). From an area where neither the photoresists 625 nor thephotoresists 626 were formed, the first hard mask film 612 is exposedafter the dry etching. The second hard mask film 613 are processed bytwo stages of dry etching, and remaining film thickness thereof in areasunder which the rectifying element portions of the four-terminal switchwith rectifying elements are to be formed, remaining film thicknessthereof in an area on the four-terminal switch with rectifying elementsexcept the areas under which the rectifying element portions are to beformed and an area under which the three-terminal switch is to beformed, and remaining film thickness thereof in an area other than thoseare 100 nm, 40 nm, and 0 nm, respectively. Although the first hard maskfilm 612 in an area where the first hard mask film 612 is exposed ispreferably not dry-etched, the first hard mask film 612 may be etched byapproximately several nm.

Step 11

Using the second hard mask film 613 as a mask, in a manner in which ashape of the processed second hard mask film 613 is transferred ontolower layers, the first hard mask film 612, the third electrode 611, therectifying layer 608, the second electrode 610, and the ion conductivelayer 609 are dry-etched in a continuous manner. This dry etching causesa rectifying layer 608 a, a second electrode 610 a, and an ionconductive layer 609 a to be formed to an area where the four-terminalswitch with rectifying elements is to be formed and a rectifying layer608 b, a second electrode 610 b, and an ion conductive layer 609 b to beformed to an area where the three-terminal switch is to be formed ((c)of FIG. 8). On this occasion, the second hard mask film 613, the firsthard mask film 612, and the third electrode 611 in the area where thethree-terminal switch is to be formed are etched and removed. Inparticular, the third electrode 611 is removed in the area where thethree-terminal switch is to be formed. Note that the rectifying layer608 b may remain or be removed in the area where the three-terminalswitch is to be formed. In the area where the four-terminal switch withrectifying elements is to be formed, the second hard mask film 613, thefirst hard mask film 612, and the third electrode 611 remain only inareas where the rectifying elements are to be formed. The second hardmask film 613 in the areas where the rectifying elements are to beformed may be removed. An area where the rectifying elements are notformed in the area where the four-terminal switch with rectifyingelements is to be formed is in the same condition as the area where thethree-terminal switch is to be formed, and, from the area where therectifying elements are not formed, the second hard mask film 613, thefirst hard mask film 612, and the third electrode 611 are etched andremoved. The rectifying layer 608 b may remain or be removed. In thearea where neither the photoresists 625 nor the photoresists 626 wereformed in the steps 7 and 9, all the layers down to the second electrode610 and the ion conductive layer 609 are removed by etching. After thedry etching, the barrier insulating film 607 may be etched by at mostapproximately several nm.

For example, when being made of titanium nitride, the third electrode611 and the upper layer of the second electrode 610 can be processed byCl₂-based RIE, and, when being made of an alloy of ruthenium andtitanium, the lower layer of the second electrode 610 can beRIE-processed using a Cl₂/O₂ gas mixture. In addition, in the etching ofthe ion conductive layer 609, the dry etching is required to be stoppedat the upper surface of the barrier insulating film 607 layered underthe ion conductive layer 609. When the ion conductive layer 609 is aSiOCH-based polymer film containing silicon, oxygen, carbon, andhydrogen and the barrier insulating film 607 is a silicon nitride filmor a silicon carbonitride film, the ion conductive layer 609 and thebarrier insulating film 607 can be RIE-processed by adjusting etchingconditions by use of a CF₄-based gas mixture, a CF₄/Cl₂-based gasmixture, a CF₄/Cl₂/Ar-based gas mixture or the like. Use of such a hardmask RIE method enables variable resistance element portions to beprocessed without exposing the variable resistance element portions tooxygen plasma ashing for resist removal. When oxidation processing isperformed by use of oxygen plasma after the processing, it becomespossible to radiate plasma in the oxidizing plasma treatment withoutdepending on resist stripping time.

Step 12

On the barrier insulating film 607 including the first hard mask film612, the second hard mask film 613, the third electrode 611, therectifying layers 608 a and 608 b, the second electrodes 610 a and 610b, and the ion conductive layer 609 a, a protection insulating film 614(for example, a silicon nitride film or a silicon carbonitride filmhaving a thickness of 20 nm) is deposited ((d) of FIG. 8). Although theprotection insulating film 614 can be formed by the plasma-enhanced CVDmethod, the wafer is required to be maintained under reduced pressure inthe reaction chamber before the film formation and, on this occasion,oxygen desorbs from the side faces of the ion conductive layers 609 aand 609 b, which may causes an issue to arise in that leakage current inthe ion conductive layer increases. In order to inhibit such aphenomenon, it is preferable to set film forming temperature of theprotection insulating film 614 at 400° C. or lower. Further, since thewafer is exposed to a film forming gas under reduced pressure before thefilm formation, it is preferable not to use a reducing gas. For example,it is preferable to use a silicon nitride film or the like that isformed by use of a high-density plasma of a SiH₄/N₂ gas mixture at asubstrate temperature of 400° C.

Step 13

On the protection insulating film 614, an interlayer insulating film 615(for example, a silicon oxide film), a low dielectric constant film (forexample, a SiOCH film having a thickness of 150 nm) that has a lowrelative dielectric constant as a low-k insulating film 616, and aninterlayer insulating film 617 (for example, a silicon oxide film) aredeposited in this sequence. Subsequently, wiring grooves for secondwirings 618 a, 618 b, and 618 c and lower holes for vias 619 a, 619 b,and 619 c are formed, and, using a copper dual damascene wiring process,the second wirings 618 a, 618 b, and 618 c (for example, copper) and thevias 619 a, 619 b, and 619 c (for example, copper) are formed in thewiring grooves and the lower holes with second barrier metals 620 a, 620b, and 620 c (for example, tantalum nitride/tantalum) in between,respectively, at the same time. Subsequently, on the interlayerinsulating film 617 including the vias 619 a, 619 b, and 619 c, abarrier insulating film 621 (for example, a silicon nitride film) isdeposited. For forming the vias 619 a, 619 b, and 619 c, a similarprocess to that used for the lower wiring formation can be used. Theinterlayer insulating films 615, the low-k insulating film 616, and theinterlayer insulating film 617 can be formed by the plasma-enhanced CVDmethod. In order to eliminate a difference in level formed by thefour-terminal switch with rectifying elements and the three-terminalswitch, the interlayer insulating film 615 may be first depositedthickly, then planarized by scraping the upper surface thereof by theCMP method, and thereby formed in a desired film thickness.

The vias 619 a, 619 b, and 619 c are formed by being patterned throughexposure using the same photoresist mask and being etched at the sametime. At depths equivalent to heights of the respective vias 619 a, 619b, and 619 c, the third electrode 611 and the second electrode 610 b areexposed to etching and etched down in the depth direction. The firsthard mask film 612 and the second hard mask film 613 in areas where thevias 619 a and 619 b are formed are etched and removed at the time offorming the vias 619 a and 619 b. As a result, the vias 619 a and 619 bare directly connected to the third electrode 611.

The rectifying layer 608 b is etched and removed at the time of formingthe via 619 c. As a result, the via 619 c is directly connected to thesecond electrode 610 b. Use of a fluorocarbon-based etching gas that hasa low etching rate for a titanium nitride-ruthenium alloy for etching toform the vias 619 a, 619 b, and 619 c causes the etching to form thevias 619 a, 619 b, and 619 c to be stopped at the third electrode 611and the second electrode 610 b.

In this way, the semiconductor device including the four-terminal switchwith rectifying elements and the three-terminal switch within themultilayer wiring layer on the semiconductor substrate, as illustratedin FIG. 9, can be produced.

Advantageous Effect of Example Embodiment

According to the present example embodiment, it is possible to achieve asemiconductor device including the four-terminal switch 122 withrectifying elements including two rectifying elements and thethree-terminal switch 123 provided with no rectifying element in thesame wiring in a multilayer wiring structure. In the present exampleembodiment, it is possible to form the four-terminal switch 122 withrectifying elements including two rectifying elements and thethree-terminal switch 123 in the same wiring layer at the same time. Thethree-terminal switch on a power-supply line is connected to atransistor.

In the production method of the example embodiment, when a hard mask forprocessing a stack of the four-terminal switch 122 with rectifyingelements is etched, a photoresist for patterning a rectifying elementportion is not formed on the hard mask in an area where thethree-terminal switch 123 is to be formed. This configuration causesthickness of the hard mask on the three-terminal switch 123 to bereduced when etching of a rectifying element pattern for thefour-terminal switch 122 with rectifying elements is performed. As aresult, when etching for processing the stack of the four-terminalswitch 122 with rectifying elements is performed, the three-terminalswitch 123 is etched down to the upper electrode (the third electrode111) of a rectifying element, which enables the via 119 c to beconnected to the three-terminal switch 123 without interposing theremaining rectifying layer 108 b.

Further, according to the production method of the present exampleembodiment, when a multi-terminal switch including rectifying elementshas two or more rectifying elements, the upper electrode of therectifying elements is separated, which enables the two rectifyingelements to be electrically independent of each other on the switch. Useof the production method of the present example embodiment enables athree-terminal switch to be formed at the same time by use of onlyphotoresist masks and exposure steps necessary for forming amulti-terminal switch provided with rectifying elements and does notinvite an increase in a production cost.

According to the present example embodiment, it is possible to provideswitching elements having structures that are respectively suitable fora wiring changeover switch constituting a programmable logic and apower-supply line control switch. For the wiring changeover switch andthe power-supply line control switch, a multi-terminal switch includingrectifying elements that does not require a select transistor andenables area saving and a three-terminal switch that can be connected toa select transistor and is capable of controlling resistance at the timeof turning on in a variable manner can be used, respectively. Thepower-supply control switch, to which a high voltage is sometimesapplied, is capable of achieving low on-resistance by performing writingwith sufficient current and thereby maintaining high reliability. Inaddition, when power-supply voltage is required to be adjusted upon achange in operational frequency at the time of operation of aprogrammable logic, it is also possible to change the on-resistance inaccordance with the power-supply voltage.

According to the present example embodiment, it is possible to form thethree-terminal switch 123 the on-resistance of which is variable throughcurrent control by a transistor and the four-terminal switch 122 withrectifying elements that, although the on-resistance thereof isdetermined invariably, enables element area to be reduced to a greatextent within the same wiring layer at the same time. For this reason,it is possible to achieve a programmable circuit provided with aswitching element that has a low on-resistance and enables highreliability to be achieved on the power-supply line, and to provide ahighly reliable, area saving, low power consumption, and low costprogrammable logic.

Second Example Embodiment

Next, a semiconductor device according to a second example embodiment ofthe present invention and a method for producing the semiconductordevice will be described. The present example embodiment is asemiconductor device that has “a two-terminal switch with a rectifyingelement and a two-terminal switch” formed within a multilayer wiringlayer. FIG. 10 is a cross-sectional schematic view illustrating aconfiguration example of the semiconductor device of the second exampleembodiment. The present example embodiment is a semiconductor devicethat includes a two-terminal switch with a rectifying element and atwo-terminal switch within a multilayer wiring layer and the equivalentcircuit diagrams of which are illustrated in (b) of FIG. 15.

Configuration

The semiconductor device illustrated in FIG. 10 has a two-terminalswitch 722 with a rectifying element and a two-terminal switch 723within a multilayer wiring layer on a semiconductor substrate 701.

The multilayer wiring layer has an insulating stacked body in which, onthe semiconductor substrate 701, an interlayer insulating film 702, alow-k insulating film 703, an interlayer insulating film 704, a barrierinsulating film 707, a protection insulating film 714, an interlayerinsulating film 715, a low-k insulating film 716, an interlayerinsulating film 717, and a barrier insulating film 721 are stacked inthis sequence. The multilayer wiring layer has, in wiring grooves formedin the interlayer insulating film 704 and the low-k insulating film 703,first wirings 705 a and 705 b embedded with first barrier metals 706 aand 706 b in between, respectively.

Further, the multilayer wiring layer has second wirings 718 a and 718 bembedded in wiring grooves formed in the interlayer insulating film 717and the low-k insulating film 716. Furthermore, vias 719 a and 719 b areembedded in lower holes that are formed in the interlayer insulatingfilm 715, the protection insulating film 714, and a first hard mask film712. Each of pairs of the second wiring 718 a and the via 719 a and thesecond wiring 718 b and the via 719 b are integrated into one body. Inaddition, the side surfaces and the bottom surfaces of pairs of thesecond wiring 718 a and the via 719 a and the second wiring 718 b andthe via 719 b are covered by second barrier metals 720 a and 720 b,respectively.

In an opening section formed in the barrier insulating film 707, on thefirst wiring 705 a that serves as a first electrode, the wall surface ofthe opening section in the barrier insulating film 707, and the barrierinsulating film 707, an ion conductive layer 709 a, a second electrode710 a, a rectifying layer 708 a, and a third electrode 711 are stackedin this sequence and the two-terminal switch 722 with a rectifyingelement is thereby formed. In addition, on the third electrode 711 ofthe two-terminal switch 722 with a rectifying element, the first hardmask film 712 and a second hard mask film 713 are formed. Further, theupper surface and the side face of a stacked body of the ion conductivelayer 709 a, the second electrode 710 a, the rectifying layer 708 a, thethird electrode 711, the first hard mask film 712, and the second hardmask film 713 are covered by the protection insulating film 714.

The multilayer wiring layer has, in another opening section formed inthe barrier insulating film 707, on the first wiring 705 b that servesas a first electrode, the wall surface of the another opening section inthe barrier insulating film 707, and the barrier insulating film 707,the two-terminal switch 723 formed in which an ion conductive layer 709b, a second electrode 710 b, and a rectifying layer 708 b are stacked inthis sequence and the upper surface and the side face of a stacked bodyof the ion conductive layer 709 b, the second electrode 710 b, and therectifying layer 708 b covered by the protection insulating film 714.

Forming a portion of the first wiring 705 a into a lower electrode ofthe two-terminal switch 722 with a rectifying element and forming aportion of the first wiring 705 b into a lower electrode of thetwo-terminal switch 723, while simplifying the number of process steps,enable electrode resistance to be reduced. Only generating a mask set ofat least three photoresist masks (three PRs) as additional process stepsto a regular copper damascene wiring process enables the two-terminalswitch 722 with a rectifying element and the two-terminal switch 723 tobe provided in the same wiring layer, which enables reduction in elementresistance and cost reduction to be achieved at the same time.

The two-terminal switch 722 with a rectifying element has the ionconductive layer 709 a in direct contact with the first wiring 705 a ina region in the opening section formed in the barrier insulating film707. A metal constituting a portion of the ion conductive layer 709 adiffuses into the first wiring 705 a and thereby forms an alloy layer.

The two-terminal switch 723 has the ion conductive layer 709 b in directcontact with the first wiring 705 b in a region in the another openingsection formed in the barrier insulating film 707. A metal constitutinga portion of the ion conductive layer 709 b diffuses into the firstwiring 705 b and thereby forms an alloy layer.

The two-terminal switch 722 with a rectifying element has the rectifyinglayer 708 a on the second electrode 710 a, and the rectifying layer 708a is in contact with the third electrode 711 at the upper surface of therectifying layer 708 a. On the third electrode 711, the first hard maskfilm 712 and a second hard mask film 713 remain. The second hard maskfilm 713 does not have to remain.

In the two-terminal switch 722 with a rectifying element, the via 719 aand the third electrode 711 are electrically connected to each otherwith the second barrier metal 720 a in between, on the third electrode711. The two-terminal switch 722 with a rectifying element is on/offcontrolled by applying voltage or flowing current between the secondelectrode 710 a and the first wiring 705 a with the rectifying layer 708a in between, such as being on/off controlled by use of electric fielddiffusion of metal ions supplied from a metal forming the first wiring705 a into the ion conductive layer 709 a. On this occasion,on-resistance is determined by current in the rectifying layer 708 a.

In the two-terminal switch 723, the via 719 b and the second electrode710 b are electrically connected to each other with the second barriermetal 720 b in between, on the second electrode 710 b. The rectifyinglayer 708 b may remain on the second electrode 710 b or may be removedwhen etching is performed in a production process of the two-terminalswitch 723. The two-terminal switch 723 is on/off controlled by applyingvoltage or flowing current, such as being on/off controlled by use ofelectric field diffusion of metal ions supplied from a metal forming thefirst wiring 705 b into the ion conductive layer 709 b.

The semiconductor substrate 701 is a substrate on which semiconductorelements are formed. For the semiconductor substrate 701, as with thefirst example embodiment, substrates, such as a silicon substrate, asingle crystal substrate, an SOI substrate, a TFT substrate, a substratefor liquid crystal production and the like can be used.

The interlayer insulating film 702 is an insulating film that is formedon the semiconductor substrate 701. For the interlayer insulating film702, as with the first example embodiment, for example, a silicon oxidefilm, a SiOC film or the like can be used. The interlayer insulatingfilm 702 may be a stack of a plurality of insulating films.

For the low-k insulating film 703, a low dielectric constant film (forexample, a SiOCH film) or the like that has a lower relative dielectricconstant than a silicon oxide film is used. The low-k insulating film703 is an insulating film that is interposed between the interlayerinsulating films 702 and 704 and has a low dielectric constant. In thelow-k insulating film 703, wiring grooves for embedding the firstwirings 705 a and 705 b are formed. In the wiring grooves in the low-kinsulating film 703, the first wirings 705 a and 705 b are embedded withthe first barrier metals 706 a and 706 b in between, respectively.

The interlayer insulating film 704 is an insulating film that is formedon the low-k insulating film 703. For the interlayer insulating film704, as with the first example embodiment, for example, a silicon oxidefilm, a SiOC film, or the like can be used. The interlayer insulatingfilm 704 may be a stack of a plurality of insulating films. In theinterlayer insulating film 704, wiring grooves for embedding the firstwirings 705 a and 705 b are formed. In the wiring grooves in theinterlayer insulating film 704, the first wirings 705 a and 705 b areembedded with the first barrier metals 706 a and 706 b in between,respectively.

The first wiring 705 a is a wiring that is embedded in the wiring grooveformed in the interlayer insulating film 704 and the low-k insulatingfilm 703 with the first barrier metals 706 a and 706 b in between. Thefirst wiring 705 a also serves as the lower electrode of thetwo-terminal switch 722 with a rectifying element and is in directcontact with the ion conductive layer 709 a. The upper surface of theion conductive layer 709 a is in direct contact with the secondelectrode 710 a. As a metal constituting the first wiring 705 a, a metalthat can diffuse and be ion-conducted in the ion conductive layer 709 ais used and, for example, copper or the like can be used. The metal (forexample, copper) constituting the first wiring 705 a may be alloyed withaluminum.

The first wiring 705 b is a wiring that is embedded in the wiring grooveformed in the interlayer insulating film 704 and the low-k insulatingfilm 703 with the first barrier metal 706 b in between. The first wiring705 b also serves as the lower electrode of the two-terminal switch 723and is in direct contact with the ion conductive layer 709 b. The uppersurface of the ion conductive layer 709 b is in direct contact with thesecond electrode 710 b. As a metal constituting the first wiring 705 b,a metal that can diffuse and be ion-conducted in the ion conductivelayer 709 b is used and, for example, copper or the like can be used.The metal (for example, copper) constituting the first wiring 705 b maybe alloyed with aluminum.

The first barrier metals 706 a and 706 b are conductive films having abarrier property. The first barrier metals 706 a and 706 b, in order toprevent the metal constituting the first wirings 705 a and 705 b fromdiffusing into the interlayer insulating film 704 and lower layers,covers the side surfaces and the bottom surfaces of the respectivewirings. When the first wirings 705 a and 705 b are constituted bymetallic elements including copper as a main component, a refractorymetal, a nitride thereof or the like, such as tantalum, tantalumnitride, titanium nitride, and tungsten carbonitride, or a stacked filmthereof can be used for the first barrier metals 706 a and 706 b.

The barrier insulating film 707 is formed on the interlayer insulatingfilm 704 including the first wirings 705 a and 705 b. This configurationenables the barrier insulating film 707 to have roles of preventing themetal (for example, copper) forming the first wirings 705 a and 705 bfrom being oxidized, preventing the metal forming the first wirings 705a and 705 b from diffusing into the interlayer insulating film 715, andworking as an etching stop layer at the time of processing the thirdelectrode 711, the rectifying layers 708 a and 708 b, the secondelectrodes 710 a and 710 b, and the ion conductive layers 709 a and 709b. For the barrier insulating film 707, for example, a SiC film, asilicon carbonitride film, a silicon nitride film, a stacked structurethereof or the like can be used. The barrier insulating film 707 ispreferably made of the same material as the protection insulating film714 and the first hard mask film 712.

The ion conductive layers 709 a and 709 b are films the resistance ofwhich changes. For the ion conductive layers 709 a and 709 b, a materialthe resistance of which changes due to action (diffusion, ionicconduction, or the like) of metal ions generated from the metal formingthe first wirings 705 a and 705 b (lower electrodes) can be used. Whenresistance change in association with switching to an on-state isachieved through deposition of a metal by reduction of metal ions, afilm capable of conducting ions is used for the ion conductive layers709 a and 709 b.

The ion conductive layers 709 a and 709 b are respectively constitutedby stacked structures of ion conductive layers that are made of of ametal oxide and are in contact with the first wirings 705 a and 705 band ion conductive layers that are made of a polymer and are in contactwith the second electrodes 710 a and 710 b.

The ion conductive layer made of a polymer in each of the ion conductivelayers 709 a and 709 b is formed using a plasma-enhanced CVD method. Rawmaterial of cyclic organosiloxane and helium, which is a carrier gas,are flowed into a reaction chamber, and, when the supply of both thecyclic organosiloxane and helium has stabilized and pressure in thereaction chamber has become constant, application of Radio Frequency(RF) electric power is started. The amount of supply of the raw materialis set at 10 to 200 sccm, and 500 sccm helium is supplied via a rawmaterial vaporizer.

The ion conductive layer made of a metal oxide in each of the ionconductive layers 709 a and 709 b has a plurality of roles. One role isto prevent the metal forming the first wirings 705 a and 705 b fromdiffusing into the ion conductive layer made of a polymer due toapplication of heat and plasma during deposition of the ion conductivelayer made of a polymer. Another role is to prevent the first wirings705 a and 705 b from being oxidized and becoming easily accelerated todiffuse into the ion conductive layer made of a polymer. A metal, suchas zirconium, hafnium, aluminum and titanium, that forms the ionconductive layer made of a metal oxide, after film formation of themetal that constitutes the ion conductive layer made of a metal oxide,is exposed to an oxygen atmosphere under reduced pressure in a filmforming chamber for the ion conductive layer made of a polymer andbecomes zirconium oxide, hafnium oxide, aluminum oxide, or titaniumoxide, thereby becoming a portion of each of the ion conductive layers709 a and 709 b. An optimum thickness of a metal film that forms the ionconductive layer made of a metal oxide is 0.5 to 1 nm. The metal filmthat is used for forming the ion conductive layer made of a metal oxidemay form a stack or a single layer. Film formation of the metal filmthat is used for forming the ion conductive layer made of a metal oxideis preferably performed by sputtering. Metal atoms or ions havingacquired energy through sputtering plunge and diffuse into the firstwirings 705 a and 705 b and form alloy layers.

The ion conductive layer 709 a is formed on the first wiring 705 a,tapered surfaces formed in the opening section in the barrier insulatingfilm 707, and the barrier insulating film 707. The ion conductive layer709 b is formed on the first wiring 705 b, tapered surfaces formed inthe another opening section in the barrier insulating film 707, and thebarrier insulating film 707.

The second electrodes 710 a and 710 b are upper electrodes of thetwo-terminal switch 722 with a rectifying element and the two-terminalswitch 723 and are in direct contact with the ion conductive layers 709a and 709 b, respectively.

For the second electrodes 710 a and 710 b, a ruthenium alloy containingtitanium, tantalum, zirconium, hafnium, aluminum or the like is used.Ruthenium is a metal that is harder to ionize than the metal forming thefirst wirings 705 a and 705 b and is hard to diffuse and beion-conducted in the ion conductive layers 709 a and 709 b. Titanium,tantalum, zirconium, hafnium, or aluminum that is added to a rutheniumalloy has a good adhesiveness with the metal forming the first wirings705 a and 705 b. As a metal that constitutes the second electrodes 710 aand 710 b and is added to ruthenium, it is preferable to select a metalthat has a standard Gibbs energy of formation of a process of generatingmetal ions from the metal (oxidation process) larger than ruthenium inthe negative direction. Because of having a standard Gibbs energy offormation of a process of generating metal ions from a metal (oxidationprocess) larger than ruthenium in the negative direction and being morelikely to spontaneously react chemically than ruthenium, titanium,tantalum, zirconium, hafnium, aluminum and the like are highly reactive.For this reason, in the ruthenium alloy that forms the second electrodes710 a and 710 b, alloying titanium, tantalum, zirconium, hafnium,aluminum or the like with ruthenium improves adhesiveness thereof withmetal cross-links formed by the metal forming the first wirings 705 aand 705 b.

On the other hand, an additive metal itself like titanium, tantalum,zirconium, hafnium, aluminum or the like, not alloyed with ruthenium,becomes too highly reactive, which causes a transition to an “OFF” statenot to occur. While a transition from an “ON” state to an “OFF” stateproceeds through oxidation reaction (dissolution reaction) of metalcross-links, when a metal constituting the second electrodes 710 a and710 b has a standard Gibbs energy of formation of a process ofgenerating metal ions from the metal (oxidation process) larger, in thenegative direction, than the metal forming the first wirings 705 a and705 b, the oxidation reaction of the metal constituting the secondelectrodes 710 a and 710 b proceeds faster than the oxidation reactionof metal cross-links formed by the metal forming the first wirings 705 aand 705 b, which causes a transition to the “OFF” state not to occur.

For this reason, a metal material that is used to form the metalconstituting the second electrodes 710 a and 710 b is required to bealloyed with ruthenium that has a standard Gibbs energy of formation ofa process of generating metal ions from the metal (oxidation process)smaller than copper in the negative direction.

Further, when copper, which is a component of metal cross-links, mixeswith the metal constituting the second electrodes 710 a and 710 b, aneffect of adding a metal having a large standard Gibbs energy offormation in the negative direction is reduced. For this reason, amaterial having a barrier property against copper and copper ions ispreferable as a metal added to ruthenium. Such materials include, forexample, tantalum and titanium. On the other hand, it has been revealedthat, the larger the amount of additive metal is, the more stable an“ON” state becomes, and even an addition of only 5 atm % metal improvesthe stability. In particular, a case of using titanium as an additivemetal excels in transition to an off-state and stability of an on-state,and it is particularly preferable that an alloy of ruthenium andtitanium be used as the metal constituting the second electrodes 710 aand 710 b and a content of titanium be set at a value within a rangefrom 20 atm % to 30 atm %. A content of ruthenium in the ruthenium alloyis preferably set at a value of 60 atm % or higher and 90 atm % orlower.

For forming a ruthenium alloy, it is preferable to use a sputteringmethod. When an alloy is film-formed using a sputtering method, thesputtering methods include a method of using a target made of an alloyof ruthenium and the first metal, a co-sputtering method of sputtering aruthenium target and a first metal target in the same chamber at thesame time, and an intermixing method in which a thin film of the firstmetal is formed in advance, ruthenium is film-formed on the thin film bya sputtering method, and the first metal and the ruthenium are alloyedwith energy of colliding atoms. Use of the co-sputtering method and theintermixing method enables composition of an alloy to be altered. Whenthe intermixing method is employed, it is preferable that, afterruthenium film formation has been finished, heat treatment at atemperature of 400° C. or lower be performed for “planarization” of themixed state of metals.

The second electrodes 710 a and 710 b preferably have a two-layerstructure. When the sides of the second electrodes 710 a and 710 b incontact with the ion conductive layers 709 a and 709 b are made of aruthenium alloy, the sides of the second electrodes 710 a and 710 b incontact with the rectifying layers 708 a and 708 b serve as lowerelectrodes of the rectifying elements. As a metal species, a metalnitride, such as titanium nitride and tantalum nitride, that isdifficult to be oxidized, easy to process, and the work function ofwhich is adjustable by adjusting composition thereof can be used.

Titanium and tantalum may also be used as long as being able to inhibitoxidation at boundary faces of the second electrodes 710 a and 710 bwith the rectifying layers 708 a and 708 b. Titanium nitride, tantalumnitride, titanium, or tantalum is film-formed on the ruthenium alloylayer by a sputtering method in a continuous vacuum process. Whentitanium or tantalum is nitrided, the nitride is film-formed byintroducing nitrogen into a chamber and using a reactive sputteringmethod.

The rectifying layers 708 a and 708 b are layers that have a bipolarrectification effect and have a characteristic in which currentincreases in a non-linear manner with respect to applied voltage. APoole-Frenkel type insulating film, a Schottky type insulating film, athreshold switching type volatile variable-resistance film, or the likecan be used as the rectifying layers 708 a and 708 b. For example, afilm containing any of titanium oxide, tungsten oxide, molybdenum oxide,hafnium oxide, aluminum oxide, zircon oxide, yttrium oxide, manganeseoxide, niobium oxide, silicon nitride, silicon carbonitride, siliconoxide, and amorphous silicon can be used as the rectifying layers 708 aand 708 b. In particular, constituting a stack by stacking amorphoussilicon, silicon nitride, and amorphous silicon in this sequence enablesexcellent non-linearity to be generated. By, by means of interposing asilicon nitride film between amorphous silicon films, causingcomposition of a portion of the silicon nitride film to be brought to astate in which nitrogen is deficient from the stoichiometric ratio andthereby reducing differences in barrier heights with the secondelectrode 710 a and the third electrode 711, it is possible tofacilitate tunneling current to flow to the silicon nitride at the timeof high voltage application. As a result, a non-linear current change isgenerated.

The third electrode 711 is a metal that serves as an upper electrode ofthe rectifying element, and, for example, tantalum, titanium, tungsten,a nitride thereof or the like can be used for the third electrode 711.In order to make current-voltage characteristics of the rectifyingelement symmetrical in both positive and negative sides, it ispreferable to use the same material as that of the second electrode 710a for the third electrode 711. The third electrode 711 also has afunction as an etching stop layer when the via 719 a is electricallyconnected onto the second electrode 710 a. Thus, it is preferable thatthe third electrode 711 have a low etching rate for plasma of afluorocarbon-based gas that is used in etching of the interlayerinsulating film 715. For forming the third electrode 711, it ispreferable to use a sputtering method. When a metal nitride isfilm-formed using a sputtering method, it is preferable to use areactive sputtering method in which a metal target is vaporized usingplasma of a gas mixture of nitrogen and argon. A metal vaporized fromthe metal target reacts with nitrogen and forms a metal nitride, whichis film-formed on a substrate.

The third electrode 711 is present only on the two-terminal switch 722with a rectifying element in which a rectifying element is formed, andis not present on the two-terminal switch 723.

The first hard mask film 712 is a film that serves as a hard mask filmand a passivation film when the third electrode 711, the secondelectrodes 710 a and 710 b, the rectifying layers 708 a and 708 b, andthe ion conductive layers 709 a and 709 b are etched. For the first hardmask film 712, as with the first example embodiment, for example,silicon nitride, silicon oxide or the like, or a stack thereof can beused. The first hard mask film 712 preferably includes the same materialas the protection insulating film 714 and the barrier insulating film707.

The second hard mask film 713 is a film that serves as a hard mask filmwhen the third electrode 711, the second electrodes 710 a and 710 b, therectifying layers 708 a and 708 b, and the ion conductive layers 709 aand 709 b are etched. For the second hard mask film 713, as with thefirst example embodiment, for example, silicon nitride, silicon oxide orthe like, or a stack thereof can be used.

As with the first example embodiment described above, based on a shapeof the second hard mask film 713, the two-terminal switch 722 with arectifying element and the two-terminal switch 723 are formeddifferently from each other. On the barrier insulating film 707 of thetwo-terminal switch 722 with a rectifying element and the two-terminalswitch 723, the ion conductive layers 709 a and 709 b, the secondelectrodes 710 a and 710 b, the rectifying layers 708 a and 708 b, thethird electrode 711, the first hard mask film 712, and the second hardmask film 713 are film-formed. Subsequently, the second hard mask film713 is processed through two rounds of patterning and etching asillustrated in (c) of FIG. 7 to (b) of FIG. 8 in the first exampleembodiment. In a manner in which a shape of the second hard mask film713, formed in this way, is transferred onto the two-terminal switch 722with a rectifying element, one rectifying element is formed on thesecond electrode 710 a.

That is, a stacked structure for the two-terminal switch 722 with arectifying element is film-formed once on the whole wafer, and, on anelement portion to which the two-terminal switch 723 is to be formed,patterning for forming a rectifying element portion in the two-terminalswitch 722 with a rectifying element is configured not to be performed(a resist is configured not to be left). This configuration causesthickness of a portion of the second hard mask film 713 on thetwo-terminal switch 723 to be reduced, as illustrated in (d) of FIG. 7in the first example embodiment. Subsequently, performing etchingenables a portion of the third electrode 711 on the two-terminal switch723 to be removed. That is, an area on the two-terminal switch 723 isbrought into the same condition as an area on the two-terminal switch722 with a rectifying element except an area under which the rectifyingelement is formed. The rectifying layer 708 b may or does not have toremain on the second electrode 710 a of the two-terminal switch 723. Inaddition, the first hard mask film 712 and the second hard mask film 713do not remain on the two-terminal switch 723.

The protection insulating film 714 is an insulating film that hasfunctions of preventing the two-terminal switch 722 with a rectifyingelement and the two-terminal switch 723 from being damaged and furtherpreventing desorption of oxygen from the ion conductive layers 709 a and709 b. For the protection insulating film 714, as with the first exampleembodiment, for example, silicon nitride, silicon carbonitride or thelike can be used. The protection insulating film 714 is preferably madeof the same material as the first hard mask film 712 and the barrierinsulating film 707. In the case of being made of the same material, theprotection insulating film 714 is integrated into one body with thebarrier insulating film 707 and the first hard mask film 712 andadhesiveness of boundary faces thereamong is thereby improved, whichenables the two-terminal switch 722 with a rectifying element and thetwo-terminal switch 723 to be protected more securely.

The interlayer insulating film 715 is an insulating film that is formedon the protection insulating film 714. For the interlayer insulatingfilm 715, as with the first example embodiment, for example, a siliconoxide film, a SiOC film or the like can be used. The interlayerinsulating film 715 may be a stack of a plurality of insulating films.The interlayer insulating film 715 may be made of the same material asthe interlayer insulating film 717. In the interlayer insulating film715, lower holes for embedding the vias 719 a and 719 b are formed, and,in the lower holes, the vias 719 a and 719 b are embedded with thesecond barrier metals 720 a and 720 b in between, respectively.

For the low-k insulating film 716, as with the first example embodiment,a low dielectric constant film (for example, a SiOCH film) or the likethat has a lower relative dielectric constant than a silicon oxide filmis used. The low-k insulating film 716 is an insulating film that isinterposed between the interlayer insulating films 715 and 717 and has alow dielectric constant. In the low-k insulating film 716, wiringgrooves for embedding the second wirings 718 a and 718 b are formed. Inthe wiring grooves in the low-k insulating film 716, the second wirings718 a and 718 b are embedded with the second barrier metals 720 a and720 b in between, respectively.

The interlayer insulating film 717 is an insulating film that is formedon the low-k insulating film 716. For the interlayer insulating film717, as with the first example embodiment, for example, a silicon oxidefilm, a SiOC film, a low dielectric constant film (for example, a SiOCHfilm) or the like that has a lower relative dielectric constant than asilicon oxide film can be used. The interlayer insulating film 717 maybe a stack of a plurality of insulating films. The interlayer insulatingfilm 717 may be made of the same material as the interlayer insulatingfilm 715. In the interlayer insulating film 717, wiring grooves forembedding the second wirings 718 a and 718 b are formed. In the wiringgrooves in the interlayer insulating film 717, the second wirings 718 aand 718 b are embedded with the second barrier metals 720 a and 720 b inbetween, respectively.

The second wirings 718 a and 718 b are wirings that are embedded in thewiring grooves formed in the interlayer insulating film 717 and thelow-k insulating film 716 with the second barrier metals 720 a and 720 bin between, respectively. The second wirings 718 a and 718 b areintegrated into one body with the vias 719 a and 719 b, respectively.

The via 719 a is embedded in the lower hole formed in the interlayerinsulating film 715, the protection insulating film 714, the first hardmask film 712, and the second hard mask film 713 with the second barriermetal 720 a in between. The via 719 b is embedded in the lower holeformed in the interlayer insulating film 715 and the protectioninsulating film 714 with the second barrier metal 720 b in between.

The via 719 a is electrically connected to the third electrode 711 viathe second barrier metal 720 a. The via 719 b is electrically connectedto the second electrode 710 b via the second barrier metal 720 b. Forthe second wirings 718 a and 718 b and the vias 719 a and 719 b, forexample, copper can be used.

The second barrier metals 720 a and 720 b are conductive films thatcover the side surfaces and the bottom surfaces of the second wirings718 a and 718 b and the vias 719 a and 719 b, respectively and have abarrier property. The second barrier metals 720 a and 720 b prevent ametal forming the second wirings 718 a and 718 b (including the vias 719a and 719 b) from diffusing into the interlayer insulating films 715 and717 and lower layers.

When the second wirings 718 a and 718 b and the vias 719 a and 719 b areconstituted by metallic elements including copper as a main component, arefractory metal, a nitride thereof or the like, such as tantalum,tantalum nitride, titanium nitride, and tungsten carbonitride, or astacked film thereof can be used for the second barrier metals 720 a and720 b.

The barrier insulating film 721 is an insulating film that is formed onthe interlayer insulating film 717 including the second wirings 718 aand 718 b. The barrier insulating film 721 has roles of preventing themetal (for example, copper) forming the second wirings 718 a and 718 bfrom being oxidized and preventing the metal forming the second wirings718 a and 718 b from diffusing into upper layers. For the barrierinsulating film 721, for example, a silicon carbonitride film, a siliconnitride film, a stacked structure thereof, or the like can be used.

Advantageous Effect of Example Embodiment

According to the present example embodiment, it is possible to achieve asemiconductor device including the two-terminal switch 722 with arectifying element including one rectifying element and the two-terminalswitch 723 provided with no rectifying element in the same wiring in amultilayer wiring structure. In the present example embodiment, it ispossible to form the two-terminal switch 722 with a rectifying elementincluding one rectifying element and the two-terminal switch 723 in thesame wiring layer at the same time.

Third Example Embodiment

Next, a semiconductor device according to a third example embodiment anda method for producing the semiconductor device will be described. Thepresent example embodiment is a semiconductor device that has “afour-terminal switch with rectifying elements and a two-terminal switch”formed within a multilayer wiring layer. FIG. 11 is a cross-sectionalschematic view illustrating a configuration example of the semiconductordevice of the third example embodiment. The present example embodimentis a semiconductor device that includes a four-terminal switch withrectifying elements and a two-terminal switch within a multilayer wiringlayer and the equivalent circuit diagrams of which are illustrated in(c) of FIG. 15.

Configuration

The semiconductor device illustrated in FIG. 11 has a four-terminalswitch 822 with rectifying elements and a two-terminal switch 823 withina multilayer wiring layer on a semiconductor substrate 801.

The multilayer wiring layer has an insulating stacked body in which, onthe semiconductor substrate 801, an interlayer insulating film 802, alow-k insulating film 803, an interlayer insulating film 804, a barrierinsulating film 807, a protection insulating film 814, an interlayerinsulating film 815, a low-k insulating film 816, an interlayerinsulating film 817, and a barrier insulating film 821 are stacked inthis sequence. The multilayer wiring layer has, in wiring grooves formedin the interlayer insulating film 804 and the low-k insulating film 803,first wirings 805 a and 805 b embedded with first barrier metals 806 aand 806 b in between, respectively. In addition, the multilayer wiringlayer has, in a wiring groove formed in the interlayer insulating film804 and the low-k insulating film 803, a first wiring 805 c embeddedwith a first barrier metal 806 c in between.

Further, the multilayer wiring layer has second wirings 818 a, 818 b,and 818 c embedded in wiring grooves formed in the interlayer insulatingfilm 817 and the low-k insulating film 816. Furthermore, vias 819 a, 819b, and 819 c are embedded in lower holes that are formed in theinterlayer insulating film 815, the protection insulating film 814, anda first hard mask film 812. Each of pairs of the second wiring 818 a andthe via 819 a, the second wiring 818 b and the via 819 b, and the secondwiring 818 c and the via 819 c are integrated into one body. Inaddition, the side surfaces and the bottom surfaces of pairs of thesecond wiring 818 a and the via 819 a, the second wiring 818 b and thevia 819 b, and the second wiring 818 c and the via 819 c are covered bysecond barrier metals 820 a, 820 b, and 820 c, respectively.

In an opening section formed in the barrier insulating film 807, on thefirst wirings 805 a and 805 b that serve as first electrodes, a portionof the interlayer insulating film 804 flanked by the first wirings 805 aand 805 b, the wall surface of the opening section in the barrierinsulating film 807, and the barrier insulating film 807, an ionconductive layer 809 a, a second electrode 810 a, a rectifying layer 808a, and a third electrode 811 are stacked in this sequence and thefour-terminal switch 822 with rectifying elements is thereby formed. Inaddition, on the third electrode 811, the first hard mask film 812 and asecond hard mask film 813 are formed. Further, the upper surface and theside face of a stacked body of the ion conductive layer 809 a, thesecond electrode 810 a, the rectifying layer 808 a, the third electrode811, the first hard mask film 812, and the second hard mask film 813 arecovered by the protection insulating film 814.

The multilayer wiring layer has, in another opening section formed inthe barrier insulating film 807, on the first wiring 805 c that servesas a first electrode, the wall surface of the another opening section inthe barrier insulating film 807, and the barrier insulating film 807,the two-terminal switch 823 formed in which an ion conductive layer 809b, a second electrode 810 b, and a rectifying layer 808 b are stacked inthis sequence and the upper surface and the side face of a stacked bodyof the ion conductive layer 809 b and the second electrode 810 b coveredby the protection insulating film 814.

Forming portions of the first wirings 805 a and 805 b into lowerelectrodes of the four-terminal switch 822 with rectifying elements andforming a portion of the first wiring 805 c into a lower electrode ofthe two-terminal switch 823, while simplifying the number of processsteps, enable electrode resistance to be reduced. Only generating a maskset of at least three PRs as additional process steps to a regularcopper damascene wiring process enables the four-terminal switch 822with rectifying elements and the two-terminal switch 823 to be providedin the same wiring layer, which enables reduction in element resistanceand cost reduction to be achieved at the same time.

The four-terminal switch 822 with rectifying elements has the ionconductive layer 809 a in direct contact with the first wirings 805 aand 805 b in regions in the opening section formed in the barrierinsulating film 807. A metal constituting a portion of the ionconductive layer 809 a diffuses into the first wirings 805 a and 805 band thereby forms alloy layers.

The two-terminal switch 823 has the ion conductive layer 809 b in directcontact with the first wiring 805 c in a region in the another openingsection formed in the barrier insulating film 807. A metal constitutinga portion of the ion conductive layer 809 b diffuses into the firstwiring 805 c and thereby forms an alloy layer.

The four-terminal switch 822 with rectifying elements has the rectifyinglayer 808 a on the second electrode 810 a, and the rectifying layer 808a is in contact with the third electrode 811 at the upper surface of therectifying layer 808 a. The third electrode 811 of the four-terminalswitch 822 with rectifying elements is electrically separated into tworegions by etching. On this occasion, the rectifying layer 808 a may beseparated into two regions as with the third electrode 811 or does nothave to be separated. On the third electrode 811, the first hard maskfilm 812 and the second hard mask film 813, which are separated as withthe third electrode 811, remain. The second hard mask film 813 does nothave to remain.

In the four-terminal switch 822 with rectifying elements, the vias 819 aand 819 b and the third electrode 811 are electrically connected to eachother with the second barrier metals 820 a and 820 b in between,respectively, on the third electrode 811.

The four-terminal switch 822 with rectifying elements is on/offcontrolled by applying voltage or flowing current between the secondelectrode 810 a and the first wiring 805 a or 805 b via the rectifyinglayer 808 a, such as being on/off controlled by use of electric fielddiffusion of metal ions supplied from a metal forming the first wirings805 a and 805 b into the ion conductive layer 809 a. On this occasion,on-resistance is determined by current in the rectifying layer 808 a.

In the two-terminal switch 823, the via 819 c and the second electrode810 b are electrically connected to each other with the second barriermetal 820 c in between, on the second electrode 810 b. The rectifyinglayer 808 b may remain on the second electrode 810 b or may be removedwhen etching is performed in a production process of the two-terminalswitch 823. The two-terminal switch 823 is on/off controlled by applyingvoltage or flowing current, such as being on/off controlled by use ofelectric field diffusion of metal ions supplied from a metal forming thefirst wiring 805 c into the ion conductive layer 809 b.

The semiconductor substrate 801 is a substrate on which semiconductorelements are formed. For the semiconductor substrate 801, as with thefirst example embodiment and the like, substrates, such as a siliconsubstrate, a single crystal substrate, an SOI substrate, a TFTsubstrate, a substrate for liquid crystal production, and the like canbe used.

The interlayer insulating film 802 is an insulating film that is formedon the semiconductor substrate 801. For the interlayer insulating film802, as with the first example embodiment and the like, for example, asilicon oxide film, a SiOC film or the like can be used. The interlayerinsulating film 802 may be a stack of a plurality of insulating films.

For the low-k insulating film 803, a low dielectric constant film (forexample, a SiOCH film) or the like that has a lower relative dielectricconstant than a silicon oxide film is used. The low-k insulating film803 is an insulating film that is interposed between the interlayerinsulating films 802 and 804 and has a low dielectric constant. In thelow-k insulating film 803, wiring grooves for embedding the firstwirings 805 a, 805 b, and 805 c are formed. In the wiring grooves in thelow-k insulating film 803, the first wirings 805 a, 805 b, and 805 c areembedded with the first barrier metals 806 a, 806 b, and 806 c inbetween, respectively.

The interlayer insulating film 804 is an insulating film that is formedon the low-k insulating film 803. For the interlayer insulating film804, as with the first example embodiment and the like, for example, asilicon oxide film, a SiOC film or the like can be used. The interlayerinsulating film 804 may be a stack of a plurality of insulating films.In the interlayer insulating film 804, wiring grooves for embedding thefirst wirings 805 a, 805 b, and 805 c are formed. In the wiring groovesin the interlayer insulating film 804, the first wirings 805 a, 805 b,and 805 c are embedded with the first barrier metals 806 a, 806 b, and806 c in between, respectively.

The first wirings 805 a and 805 b are wirings that are embedded in thewiring grooves formed in the interlayer insulating film 804 and thelow-k insulating film 803 with the first barrier metals 806 a and 806 bin between, respectively. The first wirings 805 a and 805 b also serveas the lower electrodes of the four-terminal switch 822 with rectifyingelements and are in direct contact with the ion conductive layer 809 a.The upper surface of the ion conductive layer 809 a is in direct contactwith the second electrode 810 a. As a metal constituting the firstwirings 805 a and 805 b, a metal that can diffuse and be ion-conductedin the ion conductive layer 809 a is used and, for example, copper orthe like can be used. The metal (for example, copper) constituting thefirst wirings 805 a and 805 b may be alloyed with aluminum.

The first wiring 805 c is a wiring that is embedded in the wiring grooveformed in the interlayer insulating film 804 and the low-k insulatingfilm 803 with the first barrier metal 806 c in between. The first wiring805 c also serves as the lower electrode of the two-terminal switch 823and is in direct contact with the ion conductive layer 809 b. The uppersurface of the ion conductive layer 809 b is in direct contact with thesecond electrode 810 b. As a metal constituting the first wiring 805 c,a metal that can diffuse and be ion-conducted in the ion conductivelayer 809 b is used and, for example, copper or the like can be used.The metal (for example, copper) constituting the first wiring 805 c maybe alloyed with aluminum.

The first barrier metals 806 a, 806 b, and 806 c are conductive filmshaving a barrier property. The first barrier metals 806 a, 806 b, and806 c, in order to prevent the metal forming the first wirings 805 a,805 b, and 805 c from diffusing into the interlayer insulating film 804and lower layers, covers the side surfaces and the bottom surfaces ofthe respective wirings. When the first wirings 805 a, 805 b, and 805 care constituted by metallic elements including copper as a maincomponent, a refractory metal, a nitride thereof or the like, such astantalum, tantalum nitride, titanium nitride, and tungsten carbonitride,or a stacked film thereof can be used for the first barrier metals 806a, 806 b, and 806 c.

The barrier insulating film 807 is formed on the interlayer insulatingfilm 804 including the first wirings 805 a, 805 b, and 805 c. Thisconfiguration enables the barrier insulating film 807 to have roles ofpreventing the metal (for example, copper) forming the first wirings 805a, 805 b, and 805 c from being oxidized, preventing the metal formingthe first wirings 805 a, 805 b, and 805 c from diffusing into theinterlayer insulating film 815, and working as an etching stop layer atthe time of processing the third electrode 811, the rectifying layers808 a and 808 b, the second electrodes 810 a and 810 b, and the ionconductive layers 809 a and 809 b. For the barrier insulating film 807,as with the first example embodiment and the like, for example, a SiCfilm, a silicon carbonitride film, a silicon nitride film, a stackedstructure thereof, or the like can be used. The barrier insulating film807 is preferably made of the same material as the protection insulatingfilm 814 and the first hard mask film 812.

The ion conductive layers 809 a and 809 b are films the resistance ofwhich changes. For the ion conductive layers 809 a and 809 b, a materialthe resistance of which changes due to action (diffusion, ionicconduction, or the like) of metal ions generated from the metal formingthe first wirings 805 a, 805 b, and 805 c (lower electrodes) can beused. When resistance change in association with switching to anon-state is achieved through deposition of a metal by reduction of metalions, a film capable of conducting ions is used for the ion conductivelayers 809 a and 809 b.

The ion conductive layers 809 a and 809 b are respectively constitutedby ion conductive layers that are made of a metal oxide and are incontact with the first wirings 805 a, 805 b, and 805 c and ionconductive layers that are made of a polymer and are in contact with thesecond electrodes 810 a and 810 b.

The ion conductive layer made of a polymer in each of the ion conductivelayers 809 a and 809 b is formed using a plasma-enhanced CVD method. Rawmaterial of cyclic organosiloxane and helium, which is a carrier gas,are flowed into a reaction chamber, and, when the supply of both thecyclic organosiloxane and helium has stabilized and pressure in thereaction chamber has become constant, application of RF electric poweris started. The amount of supply of the raw material is set at 10 to 200sccm, and 500 sccm helium is supplied via a raw material vaporizer.

The ion conductive layer made of a metal oxide in each of the ionconductive layers 809 a and 809 b has a plurality of roles. One role isto prevent the metal forming the first wirings 805 a, 805 b, and 805 cfrom diffusing into the ion conductive layer made of a polymer due toapplication of heat and plasma during deposition of the ion conductivelayer made of a polymer. Another role is to prevent the first wirings805 a, 805 b, and 805 c from being oxidized and becoming easilyaccelerated to diffuse into the ion conductive layer made of a polymer.A metal, such as zirconium, hafnium, aluminum and titanium, that formsthe ion conductive layer made of a metal oxide, after film formation ofthe metal that constitutes the ion conductive layer made of a metaloxide, is exposed to an oxygen atmosphere under reduced pressure in afilm forming chamber for the ion conductive layer made of a polymer andbecomes zirconium oxide, hafnium oxide, aluminum oxide, or titaniumoxide, thereby becoming a portion of each of the ion conductive layers809 a and 809 b. An optimum thickness of a metal film that forms the ionconductive layer made of a metal oxide is 0.5 to 1 nm. The metal filmthat is used for forming the ion conductive layer made of a metal oxidemay form a stack or a single layer. Film formation of the metal filmthat is used for forming the ion conductive layer made of a metal oxideis preferably performed by sputtering. Metal atoms or ions havingacquired energy through sputtering plunge and diffuse into the firstwirings 805 a, 805 b, and 805 c and form alloy layers.

The ion conductive layer 809 a is formed on the first wirings 805 a and805 b, a portion of the interlayer insulating film 804 flanked by thefirst wirings 805 a and 805 b, tapered surfaces formed in the openingsection in the barrier insulating film 807, and the barrier insulatingfilm 807.

The ion conductive layer 809 b is formed on the first wiring 805 c,tapered surfaces formed in the another opening section in the barrierinsulating film 807, and the barrier insulating film 807.

The second electrodes 810 a and 810 b are upper electrodes of thefour-terminal switch 822 with rectifying elements and the two-terminalswitch 823 and are in direct contact with the ion conductive layers 809a and 809 b, respectively.

For the second electrodes 810 a and 810 b, a ruthenium alloy containingtitanium, tantalum, zirconium, hafnium, aluminum or the like is used.Ruthenium is a metal that is harder to ionize than the metal forming thefirst wirings 805 a, 805 b, and 805 c and is hard to diffuse and beion-conducted in the ion conductive layers 809 a and 809 b. Titanium,tantalum, zirconium, hafnium, or aluminum that is added to a rutheniumalloy has a good adhesiveness with the metal forming the first wirings805 a, 805 b, and 805 c. As a first metal that constitutes the secondelectrodes 810 a and 810 b and is added to ruthenium, it is preferableto select a metal that has a standard Gibbs energy of formation of aprocess of generating metal ions from the metal (oxidation process)larger than ruthenium in the negative direction. Because of having astandard Gibbs energy of formation of a process of generating metal ionsfrom a metal (oxidation process) larger than ruthenium in the negativedirection and being more likely to spontaneously react chemically thanruthenium, titanium, tantalum, zirconium, hafnium, aluminum or the likeare highly reactive. For this reason, in the ruthenium alloy that formsthe second electrodes 810 a and 810 b, alloying titanium, tantalum,zirconium, hafnium, aluminum, or the like with ruthenium improvesadhesiveness thereof with metal cross-links formed by the metal formingthe first wirings 805 a, 805 b, and 805 c.

On the other hand, an additive metal itself like titanium, tantalum,zirconium, hafnium, aluminum or the like, not alloyed with ruthenium,becomes too highly reactive, which causes a transition to an “OFF” statenot to occur. While a transition from an “ON” state to an “OFF” stateproceeds through oxidation reaction (dissolution reaction) of metalcross-links, when a metal constituting the second electrodes 810 a and810 b has a standard Gibbs energy of formation of a process ofgenerating metal ions from the metal (oxidation process) larger, in thenegative direction, than the metal forming the first wirings 805 a, 805b, and 805 c, the oxidation reaction of the metal constituting thesecond electrodes 810 a and 810 b proceeds faster than the oxidationreaction of metal cross-links formed by the metal forming the firstwirings 805 a, 805 b, and 805 c, which causes a transition to the “OFF”state not to occur.

For this reason, a metal material that is used to form the metalconstituting the second electrodes 810 a and 810 b is required to bealloyed with ruthenium that has a standard Gibbs energy of formation ofa process of generating metal ions from the metal (oxidation process)smaller than copper in the negative direction.

Further, when copper, which is a component of metal cross-links, mixeswith the metal constituting the second electrodes 810 a and 810 b, aneffect of adding a metal having a large standard Gibbs energy offormation in the negative direction is reduced. For this reason, amaterial having a barrier property against copper and copper ions ispreferable as a metal added to ruthenium. Such materials include, forexample, tantalum and titanium. On the other hand, it has been revealedthat, the larger the amount of additive metal is, the more stable an“ON” state becomes, and even an addition of only 5 atm % metal improvesthe stability. In particular, a case of using titanium as an additivemetal excels in transition to an off-state and stability of an on-state,and it is particularly preferable that an alloy of ruthenium andtitanium be used as the metal constituting the second electrodes 810 aand 810 b and a content of titanium be set at a value within a rangefrom 20 atm % to 30 atm %. A content of ruthenium in the ruthenium alloyis preferably set at a value of 60 atm % or higher and 90 atm % orlower.

For forming a ruthenium alloy, it is preferable to use a sputteringmethod. When an alloy is film-formed using a sputtering method, thesputtering methods include a method of using a target made of an alloyof ruthenium and the first metal, a co-sputtering method of sputtering aruthenium target and a first metal target in the same chamber at thesame time, and an intermixing method in which a thin film of the firstmetal is formed in advance, ruthenium is film-formed on the thin film bya sputtering method, and the first metal and the ruthenium are alloyedwith energy of colliding atoms. Use of the co-sputtering method and theintermixing method enables composition of an alloy to be altered. Whenthe intermixing method is employed, it is preferable that, afterruthenium film formation has been finished, heat treatment at atemperature of 400° C. or lower be performed for “planarization” of themixed state of metals.

The second electrodes 810 a and 810 b preferably have a two-layerstructure. When the sides of the second electrodes 810 a and 810 b incontact with the ion conductive layers 809 a and 809 b are made of aruthenium alloy, the sides of the second electrodes 810 a and 810 b incontact with the rectifying layers 808 a and 808 b serve as lowerelectrodes of the rectifying elements. As a metal species, a metalnitride, such as titanium nitride and tantalum nitride, that isdifficult to be oxidized, easy to process, and the work function ofwhich is adjustable by adjusting composition thereof can be used.

Titanium and tantalum may also be used as long as being able to inhibitoxidation at boundary faces of the second electrodes 810 a and 810 bwith the rectifying layers 808 a and 808 b. Titanium nitride, tantalumnitride, titanium, or tantalum is film-formed on the ruthenium alloylayer by a sputtering method in a continuous vacuum process. Whentitanium or tantalum is nitrided, the nitride is film-formed byintroducing nitrogen into a chamber and using a reactive sputteringmethod.

The rectifying layers 808 a and 808 b are layers that have a bipolarrectification effect and have a characteristic in which currentincreases in a non-linear manner with respect to applied voltage. APoole-Frenkel type insulating film, a Schottky type insulating film, athreshold switching type volatile variable-resistance film, or the likecan be used as the rectifying layers 808 a and 808 b. For example, afilm containing any of titanium oxide, tungsten oxide, molybdenum oxide,hafnium oxide, aluminum oxide, zircon oxide, yttrium oxide, manganeseoxide, niobium oxide, silicon nitride, silicon carbonitride, siliconoxide, and amorphous silicon can be used as the rectifying layers 808 aand 808 b. In particular, constituting a stack by stacking amorphoussilicon, silicon nitride, and amorphous silicon in this sequence enablesexcellent non-linearity to be generated. By, by means of interposing asilicon nitride film between amorphous silicon films, causingcomposition of a portion of the silicon nitride film to be brought to astate in which nitrogen is deficient from the stoichiometric ratio andthereby reducing differences in barrier heights with the secondelectrode 810 a and the third electrode 811, it is possible tofacilitate tunneling current to flow to the silicon nitride at the timeof high voltage application. As a result, a non-linear current change isgenerated.

The third electrode 811 is a metal that serves as upper electrodes ofthe rectifying elements, and, for example, tantalum, titanium, tungsten,a nitride thereof, or the like can be used for the third electrode 811.In order to make current-voltage characteristics of the rectifyingelements symmetrical in both positive and negative sides, it ispreferable to use the same material as those of the second electrodes810 a and 810 b for the third electrode 811. The third electrode 811also has a function as an etching stop layer when the vias 819 a and 819b are electrically connected onto the second electrode 810 a. Thus, itis preferable that the third electrode 811 have a low etching rate forplasma of a fluorocarbon-based gas that is used in etching of theinterlayer insulating film 815. For forming the third electrode 811, itis preferable to use a sputtering method. When a metal nitride isfilm-formed using a sputtering method, it is preferable to use areactive sputtering method in which a metal target is vaporized usingplasma of a gas mixture of nitrogen and argon. A metal vaporized fromthe metal target reacts with nitrogen and forms a metal nitride, whichis film-formed on a substrate.

The third electrode 811 is present only on the four-terminal switch 822with rectifying elements in which rectifying elements are formed andseparated into two regions on the four-terminal switch 822 withrectifying elements. As a result, two rectifying elements are arrangedon the four-terminal switch 822 with rectifying elements independentlyof each other.

The first hard mask film 812 is a film that serves as a hard mask filmand a passivation film when the third electrode 811, the secondelectrodes 810 a and 810 b, the rectifying layers 808 a and 808 b, andthe ion conductive layers 809 a and 809 b are etched. For the first hardmask film 812, as with the first example embodiment and the like, forexample, a silicon nitride film, a silicon oxide film or the like, or astack thereof can be used. The first hard mask film 812 preferablyincludes the same material as the protection insulating film 814 and thebarrier insulating film 807.

The second hard mask film 813 is a film that serves as a hard mask filmwhen the third electrode 811, the second electrodes 810 a and 810 b, therectifying layers 808 a and 808 b, and the ion conductive layers 809 aand 809 b are etched. For the second hard mask film 813, for example, asilicon nitride film, a silicon oxide film or the like, or a stackthereof can be used.

Based on a shape of the second hard mask film 813, the four-terminalswitch 822 with rectifying elements and the two-terminal switch 823 areformed differently from each other. On the barrier insulating film 807of the four-terminal switch 822 with rectifying elements and thetwo-terminal switch 823, the ion conductive layers 809 a and 809 b, thesecond electrodes 810 a and 810 b, the rectifying layers 808 a and 808b, the third electrode 811, the first hard mask film 812, and the secondhard mask film 813 are film-formed. Subsequently, in a manner in which ashape of the second hard mask film 813, formed through two rounds ofpatterning and etching, is transferred onto the four-terminal switch 822with rectifying elements, two rectifying elements are formed separatedfrom each other on the second electrode 810 a in one round of etching.

That is, a stacked structure for the four-terminal switch 822 withrectifying elements is film-formed once on the whole wafer, and, on anelement portion to which the two-terminal switch 823 is to be formed,patterning for forming a rectifying element portion in the four-terminalswitch 822 with rectifying elements is configured not to be performed (aresist is configured not to be left). This configuration causesthickness of a portion of the second hard mask film 813 on thetwo-terminal switch 823 to be reduced. Subsequently, performing etchingenables a portion of the third electrode 811 on the two-terminal switch823 to be removed. That is, an area on the two-terminal switch 823 isbrought into the same condition as an area on the four-terminal switch822 with rectifying elements except an area under which the rectifyingelements are formed. The rectifying layer 808 b may or does not have toremain on the second electrode 810 a of the two-terminal switch 823. Inaddition, the first hard mask film 812 and the second hard mask film 813do not remain on the two-terminal switch 823.

The protection insulating film 814 is an insulating film that hasfunctions of preventing the four-terminal switch 822 with rectifyingelements and the two-terminal switch 823 from being damaged and furtherpreventing desorption of oxygen from the ion conductive layers 809 a and809 b. For the protection insulating film 814, for example, a siliconnitride film, a silicon carbonitride film or the like can be used. Theprotection insulating film 814 is preferably made of the same materialas the first hard mask film 812 and the barrier insulating film 807. Inthe case of being made of the same material, the protection insulatingfilm 814 is integrated into one body with the barrier insulating film807 and the first hard mask film 812 and adhesiveness of boundary facesthereamong is thereby improved, which enables the four-terminal switch822 with rectifying elements and the two-terminal switch 823 to beprotected more securely.

The interlayer insulating film 815 is an insulating film that is formedon the protection insulating film 814. For the interlayer insulatingfilm 815, for example, a silicon oxide film, a SiOC film or the like canbe used. The interlayer insulating film 815 may be a stack of aplurality of insulating films. The interlayer insulating film 815 may bemade of the same material as the interlayer insulating film 817. In theinterlayer insulating film 815, lower holes for embedding the vias 819a, 819 b, and 819 c are formed, and, in the lower holes, the vias 819 a,819 b, and 819 c are embedded with the second barrier metals 820 a, 820b, and 820 c in between, respectively.

For the low-k insulating film 816, a low dielectric constant film (forexample, a SiOCH film) or the like that has a lower relative dielectricconstant than a silicon oxide film is used. The low-k insulating film816 is an insulating film that is interposed between the interlayerinsulating films 815 and 817 and has a low dielectric constant. In thelow-k insulating film 816, wiring grooves for embedding the secondwirings 818 a, 818 b, and 818 c are formed. In the wiring grooves in thelow-k insulating film 816, the second wirings 818 a, 818 b, and 818 care embedded with the second barrier metals 820 a, 820 b, and 820 c inbetween, respectively.

The interlayer insulating film 817 is an insulating film that is formedon the low-k insulating film 816. For the interlayer insulating film817, for example, a silicon oxide film, a SiOC film, a low dielectricconstant film (for example, a SiOCH film) that has a lower relativedielectric constant than a silicon oxide film, or the like can be used.The interlayer insulating film 817 may be a stack of a plurality ofinsulating films. The interlayer insulating film 817 may be made of thesame material as the interlayer insulating film 815. In the interlayerinsulating film 817, wiring grooves for embedding the second wirings 818a, 818 b, and 818 c are formed. In the wiring grooves in the interlayerinsulating film 817, the second wirings 818 a, 818 b, and 818 c areembedded with the second barrier metals 820 a, 820 b, and 820 c inbetween, respectively.

The second wirings 818 a, 818 b, and 818 c are wirings that are embeddedin the wiring grooves formed in the interlayer insulating film 817 andthe low-k insulating film 816 with the second barrier metals 820 a, 820b, and 820 c in between, respectively. The second wirings 818 a, 818 b,and 818 c are integrated into one body with the vias 819 a, 819 b, and819 c, respectively.

The vias 819 a and 819 b are embedded in the lower holes formed in theinterlayer insulating film 815, the protection insulating film 814, thefirst hard mask film 812, and the second hard mask film 813 with thesecond barrier metals 820 a and 820 b in between, respectively. The via819 c is embedded in the lower hole formed in the interlayer insulatingfilm 815 and the protection insulating film 814 with the second barriermetal 820 c in between.

The vias 819 a and 819 b are electrically connected to the thirdelectrode 811 via the second barrier metals 820 a and 820 b,respectively. The via 819 c is electrically connected to the secondelectrode 810 b via the second barrier metal 820 c. For the secondwirings 818 a, 818 b, and 818 c and the vias 819 a, 819 b, and 819 c,for example, copper can be used.

The second barrier metals 820 a, 820 b, and 820 c are conductive filmsthat cover the side surfaces and the bottom surfaces of the secondwirings 818 a, 818 b, and 818 c and the vias 819 a, 819 b, and 819 c,respectively and have a barrier property. The second barrier metals 820a, 820 b, and 820 c prevent a metal forming the second wirings 818 a,818 b, and 818 c (including the vias 819 a, 819 b, and 819 c) fromdiffusing into the interlayer insulating films 815 and 817 and lowerlayers.

When the second wirings 818 a, 818 b, and 818 c and the vias 819 a, 819b, and 819 c are constituted by metallic elements including copper as amain component, a refractory metal, a nitride thereof or the like, suchas tantalum, tantalum nitride, titanium nitride and tungstencarbonitride, or a stacked film thereof can be used for the secondbarrier metals 820 a, 820 b, and 820 c.

The barrier insulating film 821 is an insulating film that is formed onthe interlayer insulating film 817 including the second wirings 818 a,818 b, and 818 c. The barrier insulating film 821 has roles ofpreventing the metal (for example, copper) forming the second wirings818 a, 818 b, and 818 c from being oxidized and preventing the metalforming the second wirings 818 a, 818 b, and 818 c from diffusing intoupper layers. For the barrier insulating film 821, for example, asilicon carbonitride film, a silicon nitride film, a stacked structurethereof, or the like can be used.

Advantageous Effect of Example Embodiment

According to the present example embodiment, it is possible to achieve asemiconductor device including the four-terminal switch 822 withrectifying elements including two rectifying elements and thetwo-terminal switch 823 provided with no rectifying element in the samewiring in a multilayer wiring structure. In the present exampleembodiment, it is possible to form the four-terminal switch 822 withrectifying elements including two rectifying elements and thetwo-terminal switch 823 in the same wiring layer at the same time.

Fourth Example Embodiment

Next, a semiconductor device according to a fourth example embodimentand a method for producing the semiconductor device will be described.The present example embodiment is a semiconductor device that has “atwo-terminal switch with a rectifying element and a three-terminalswitch” formed within a multilayer wiring layer. FIG. 12 is across-sectional schematic view illustrating a configuration example ofthe semiconductor device of the fourth example embodiment. The presentexample embodiment is a semiconductor device that includes atwo-terminal switch with a rectifying element and a three-terminalswitch within a multilayer wiring layer and the equivalent circuitdiagrams of which are illustrated in (a) of FIG. 16.

Configuration

The semiconductor device illustrated in FIG. 12 has a two-terminalswitch 922 with a rectifying element and a three-terminal switch 923within a multilayer wiring layer on a semiconductor substrate 901.

The multilayer wiring layer has an insulating stacked body in which, onthe semiconductor substrate 901, an interlayer insulating film 902, alow-k insulating film 903, an interlayer insulating film 904, a barrierinsulating film 907, a protection insulating film 914, an interlayerinsulating film 915, a low-k insulating film 916, an interlayerinsulating film 917, and a barrier insulating film 921 are stacked inthis sequence. The multilayer wiring layer has, in wiring grooves formedin the interlayer insulating film 904 and the low-k insulating film 903,first wirings 905 a and 905 b embedded with first barrier metals 906 aand 906 b in between, respectively.

Further, the multilayer wiring layer has second wirings 918 a and 918 bembedded in wiring grooves formed in the interlayer insulating film 917and the low-k insulating film 916. Furthermore, vias 919 a and 919 b areembedded in lower holes that are formed in the interlayer insulatingfilm 915, the protection insulating film 914, and a first hard mask film912. Each of pairs of the second wiring 918 a and the via 919 a and thesecond wiring 918 b and the via 919 b are integrated into one body. Inaddition, the side surfaces and the bottom surfaces of pairs of thesecond wiring 918 a and the via 919 a and the second wiring 918 b andthe via 919 b are covered by second barrier metals 920 a and 920 b,respectively.

In an opening section formed in the barrier insulating film 907, on thefirst wiring 905 a that serves as a first electrode, the wall surface ofthe opening section in the barrier insulating film 907, and the barrierinsulating film 907, an ion conductive layer 909 a, a second electrode910 a, a rectifying layer 908 a, and a third electrode 911 are stackedin this sequence and the two-terminal switch 922 with a rectifyingelement is thereby formed. In addition, on the third electrode 911, thefirst hard mask film 912 and a second hard mask film 913 are formed.Further, the upper surface and the side face of a stacked body of theion conductive layer 909 a, the second electrode 910 a, the rectifyinglayer 908 a, the third electrode 911, the first hard mask film 912, andthe second hard mask film 913 are covered by the protection insulatingfilm 914.

The multilayer wiring layer has, in another opening section formed inthe barrier insulating film 907, on the first wirings 905 b and 905 cthat serve as first electrodes, a portion of the interlayer insulatingfilm 904 flanked by the first wirings 905 b and 905 c, the wall surfaceof the another opening section in the barrier insulating film 907, andthe barrier insulating film 907, the three-terminal switch 923 formed inwhich an ion conductive layer 909 b, a second electrode 910 b, and arectifying layer 908 b are stacked in this sequence and the uppersurface and the side face of a stacked body of the ion conductive layer909 b and the second electrode 910 b covered by the protectioninsulating film 914.

Forming a portion of the first wiring 905 a into a lower electrode ofthe two-terminal switch 922 with a rectifying element and formingportions of the first wirings 905 b and 905 c into lower electrodes ofthe three-terminal switch 923, while simplifying the number of processsteps, enable electrode resistance to be reduced. Only generating a maskset of at least three PRs as additional process steps to a regularcopper damascene wiring process enables the two-terminal switch 922 witha rectifying element and the three-terminal switch 923 to be provided inthe same wiring layer, which enables reduction in element resistance andcost reduction to be achieved at the same time.

The two-terminal switch 922 with a rectifying element has the ionconductive layer 909 a in direct contact with the first wiring 905 a ina region in the opening section formed in the barrier insulating film907. A metal constituting a portion of the ion conductive layer 909 adiffuses into the first wiring 905 a and thereby forms an alloy layer.

The three-terminal switch 923 has the ion conductive layer 909 b indirect contact with the first wirings 905 b and 905 c in regions in theanother opening section formed in the barrier insulating film 907. Ametal constituting a portion of the ion conductive layer 909 b diffusesinto the first wirings 905 b and 905 c and thereby forms alloy layers.

The two-terminal switch 922 with a rectifying element has the rectifyinglayer 908 a on the second electrode 910 a, and the rectifying layer 908a is in contact with the third electrode 911 at the upper surface of therectifying layer 908 a. On the third electrode 911, the first hard maskfilm 912 and the second hard mask film 913 remain. The second hard maskfilm 913 does not have to remain.

In the two-terminal switch 922 with a rectifying element, the via 919 aand the third electrode 911 are electrically connected to each otherwith the second barrier metal 920 a in between, on the third electrode911.

The two-terminal switch 922 with a rectifying element is on/offcontrolled by applying voltage or flowing current between the secondelectrode 910 a and the first wiring 905 a via the rectifying layer 908a, such as being on/off controlled by use of electric field diffusion ofmetal ions supplied from a metal forming the first wiring 905 a into theion conductive layer 909 a. On this occasion, on-resistance isdetermined by current in the rectifying layer 908 a.

In the three-terminal switch 923, the via 919 b and the second electrode910 b are electrically connected to each other with the second barriermetal 920 b in between, on the second electrode 910 b. The rectifyinglayer 908 b may remain on the second electrode 910 b or may be removedwhen etching is performed in a production process of the three-terminalswitch 923. The three-terminal switch 923 is on/off controlled byapplying voltage or flowing current, such as being on/off controlled byuse of electric field diffusion of metal ions supplied from a metalforming the first wirings 905 b and 905 c into the ion conductive layer909 b.

The semiconductor substrate 901 is a substrate on which semiconductorelements are formed. For the semiconductor substrate 901, as with thefirst example embodiment and the like, substrates, such as a siliconsubstrate, a single crystal substrate, an SOI substrate, a TFTsubstrate, a substrate for liquid crystal production, and the like canbe used.

The interlayer insulating film 902 is an insulating film that is formedon the semiconductor substrate 901. For the interlayer insulating film902, for example, a silicon oxide film, a SiOC film or the like can beused. The interlayer insulating film 902 may be a stack of a pluralityof insulating films.

For the low-k insulating film 903, a low dielectric constant film (forexample, a SiOCH film) or the like that has a lower relative dielectricconstant than a silicon oxide film is used. The low-k insulating film903 is an insulating film that is interposed between the interlayerinsulating films 902 and 904 and has a low dielectric constant. In thelow-k insulating film 903, wiring grooves for embedding the firstwirings 905 a, 905 b, and 905 c are formed. In the wiring grooves in thelow-k insulating film 903, the first wirings 905 a, 905 b, and 905 c areembedded with the first barrier metals 906 a, 906 b, and 906 c inbetween, respectively.

The interlayer insulating film 904 is an insulating film that is formedon the low-k insulating film 903. For the interlayer insulating film904, for example, a silicon oxide film, a SiOC film or the like can beused. The interlayer insulating film 904 may be a stack of a pluralityof insulating films. In the interlayer insulating film 904, wiringgrooves for embedding the first wirings 905 a, 905 b, and 905 c areformed. In the wiring grooves in the interlayer insulating film 904, thefirst wirings 905 a, 905 b, and 905 c are embedded with the firstbarrier metals 906 a, 906 b, and 906 c in between, respectively.

The first wiring 905 a is a wiring that is embedded in the wiring grooveformed in the interlayer insulating film 904 and the low-k insulatingfilm 903 with the first barrier metal 906 a in between. The first wiring905 a also serves as the lower electrode of the two-terminal switch 922with a rectifying element and is in direct contact with the ionconductive layer 909 a. The upper surface of the ion conductive layer909 a is in direct contact with the second electrode 910 a. As a metalconstituting the first wirings 905 a and 905 b, a metal that can diffuseand be ion-conducted in the ion conductive layer 909 a is used and, forexample, copper or the like can be used. The metal (for example, copper)constituting the first wirings 905 a and 905 b may be alloyed withaluminum.

The first wirings 905 b and 905 c are wirings that are embedded in thewiring grooves formed in the interlayer insulating film 904 and thelow-k insulating film 903 with the first barrier metals 906 b and 906 cin between, respectively. The first wirings 905 b and 905 c also serveas the lower electrodes of the three-terminal switch 923 and are indirect contact with the ion conductive layer 909 b. The upper surface ofthe ion conductive layer 909 b is in direct contact with the secondelectrode 910 b. As a metal constituting the first wirings 905 b and 905c, a metal that can diffuse and be ion-conducted in the ion conductivelayer 909 b is used and, for example, copper or the like can be used.The metal (for example, copper) constituting the first wirings 905 b and905 c may be alloyed with aluminum.

The first barrier metals 906 a, 906 b, and 906 c are conductive filmshaving a barrier property. The first barrier metals 906 a, 906 b, and906 c, in order to prevent the metal forming the first wirings 905 a,905 b, and 905 c from diffusing into the interlayer insulating film 904and lower layers, covers the side surfaces and the bottom surfaces ofthe respective wirings. When the first wirings 905 a, 905 b, and 905 care constituted by metallic elements including copper as a maincomponent, a refractory metal, a nitride thereof or the like, such astantalum, tantalum nitride, titanium nitride, and tungsten carbonitride,or a stacked film thereof can be used for the first barrier metals 906a, 906 b, and 906 c.

The barrier insulating film 907 is formed on the interlayer insulatingfilm 904 including the first wirings 905 a, 905 b, and 905 c. Thisconfiguration enables the barrier insulating film 907 to have roles ofpreventing the metal (for example, copper) forming the first wirings 905a, 905 b, and 905 c from being oxidized, preventing the metal formingthe first wirings 905 a, 905 b, and 905 c from diffusing into theinterlayer insulating film 915, and working as an etching stop layer atthe time of processing the third electrode 911, the rectifying layers908 a and 908 b, the second electrodes 910 a and 910 b, and the ionconductive layers 909 a and 909 b. For the barrier insulating film 907,for example, a SiC film, a silicon carbonitride film, a silicon nitridefilm, a stacked structure thereof, or the like can be used. The barrierinsulating film 907 is preferably made of the same material as theprotection insulating film 914 and the first hard mask film 912.

The ion conductive layers 909 a and 909 b are films the resistance ofwhich changes. For the ion conductive layers 909 a and 909 b, a materialthe resistance of which changes due to action (diffusion, ionicconduction, or the like) of metal ions generated from the metal formingthe first wirings 905 a, 905 b, and 905 c (lower electrodes) can beused. When resistance change in association with switching to anon-state is achieved through deposition of a metal by reduction of metalions, a film capable of conducting ions is used for the ion conductivelayers 909 a and 909 b.

The ion conductive layers 909 a and 909 b are respectively constitutedby ion conductive layers that are made of a metal oxide and are incontact with the first wirings 905 a, 905 b, and 905 c and ionconductive layers that are made of a polymer and are in contact with thesecond electrodes 910 a and 910 b.

The ion conductive layer made of a polymer in each of the ion conductivelayers 909 a and 909 b is formed using a plasma-enhanced CVD method. Rawmaterial of cyclic organosiloxane and helium, which is a carrier gas,are flowed into a reaction chamber, and, when the supply of both thecyclic organosiloxane and helium has stabilized and pressure in thereaction chamber has become constant, application of RF electric poweris started. The amount of supply of the raw material is set at 10 to 200sccm, and 500 sccm helium is supplied via a raw material vaporizer.

The ion conductive layer made of a metal oxide in each of the ionconductive layers 909 a and 909 b has a plurality of roles. One role isto prevent the metal forming the first wirings 905 a, 905 b, and 905 cfrom diffusing into the ion conductive layer made of a polymer due toapplication of heat and plasma during deposition of the ion conductivelayer made of a polymer. Another role is to prevent the first wirings905 a, 905 b, and 905 c from being oxidized and becoming easilyaccelerated to diffuse into the ion conductive layer made of a polymer.A metal, such as zirconium, hafnium, aluminum and titanium, that formsthe ion conductive layer made of a metal oxide, after film formation ofthe metal that constitutes the ion conductive layer made of a metaloxide, is exposed to an oxygen atmosphere under reduced pressure in afilm forming chamber for the ion conductive layer made of a polymer andbecomes zirconium oxide, hafnium oxide, aluminum oxide, or titaniumoxide, thereby becoming a portion of each of the ion conductive layers909 a and 909 b. An optimum thickness of a metal film that forms the ionconductive layer made of a metal oxide is 0.5 to 1 nm. The metal filmthat is used for forming the ion conductive layer made of a metal oxidemay form a stack or a single layer. Film formation of the metal filmthat is used for forming the ion conductive layer made of a metal oxideis preferably performed by sputtering. Metal atoms or ions havingacquired energy through sputtering plunge and diffuse into the firstwirings 905 a, 905 b, and 905 c and form alloy layers.

The ion conductive layer 909 a is formed on the first wiring 905 a,tapered surfaces formed in the opening section in the barrier insulatingfilm 907, and the barrier insulating film 907.

The ion conductive layer 909 b is formed on the first wirings 905 b and905 c, a portion of the interlayer insulating film 904 flanked by thefirst wirings 905 b and 905 c, tapered surfaces formed in the anotheropening section in the barrier insulating film 907, and the barrierinsulating film 907.

The second electrodes 910 a and 910 b are upper electrodes of thetwo-terminal switch 922 with a rectifying element and the three-terminalswitch 923 and are in direct contact with the ion conductive layers 909a and 909 b, respectively.

For the second electrodes 910 a and 910 b, a ruthenium alloy containingtitanium, tantalum, zirconium, hafnium, aluminum or the like is used.Ruthenium is a metal that is harder to ionize than the metal forming thefirst wirings 905 a, 905 b, and 905 c and is hard to diffuse and beion-conducted in the ion conductive layers 909 a and 909 b. Titanium,tantalum, zirconium, hafnium, or aluminum that is added to a rutheniumalloy has a good adhesiveness with the metal forming the first wirings905 a, 905 b, and 905 c. As a first metal that constitutes the secondelectrodes 910 a and 910 b and is added to ruthenium, it is preferableto select a metal that has a standard Gibbs energy of formation of aprocess of generating metal ions from the metal (oxidation process)larger than ruthenium in the negative direction. Because of having astandard Gibbs energy of formation of a process of generating metal ionsfrom a metal (oxidation process) larger than ruthenium in the negativedirection and being more likely to spontaneously react chemically thanruthenium, titanium, tantalum, zirconium, hafnium, aluminum or the likeare highly reactive. For this reason, in the ruthenium alloy that formsthe second electrodes 910 a and 910 b, alloying titanium, tantalum,zirconium, hafnium, aluminum or the like with ruthenium improvesadhesiveness thereof with metal cross-links formed by the metal formingthe first wirings 905 a, 905 b, and 905 c.

On the other hand, an additive metal itself like titanium, tantalum,zirconium, hafnium, aluminum or the like, not alloyed with ruthenium,becomes too highly reactive, which causes a transition to an “OFF” statenot to occur. While a transition from an “ON” state to an “OFF” stateproceeds through oxidation reaction (dissolution reaction) of metalcross-links, when a metal constituting the second electrodes 910 a and910 b has a standard Gibbs energy of formation of a process ofgenerating metal ions from the metal (oxidation process) larger, in thenegative direction, than the metal forming the first wirings 905 a, 905b, and 905 c, the oxidation reaction of the metal constituting thesecond electrodes 910 a and 910 b proceeds faster than the oxidationreaction of metal cross-links formed by the metal forming the firstwirings 905 a, 905 b, and 905 c, which causes a transition to the “OFF”state not to occur.

For this reason, a metal material that is used to form the metalconstituting the second electrodes 910 a and 910 b is required to bealloyed with ruthenium that has a standard Gibbs energy of formation ofa process of generating metal ions from the metal (oxidation process)smaller than copper in the negative direction.

Further, when copper, which is a component of metal cross-links, mixeswith the metal constituting the second electrodes 910 a and 910 b, aneffect of adding a metal having a large standard Gibbs energy offormation in the negative direction is reduced. For this reason, amaterial having a barrier property against copper and copper ions ispreferable as a metal added to ruthenium. Such materials include, forexample, tantalum and titanium. On the other hand, it has been revealedthat, the larger the amount of additive metal is, the more stable an“ON” state becomes, and even an addition of only 5 atm % metal improvesthe stability. In particular, a case of using titanium as an additivemetal excels in transition to an off-state and stability of an on-state,and it is particularly preferable that an alloy of ruthenium andtitanium be used as the metal constituting the second electrodes 910 aand 910 b and a content of titanium be set at a value within a rangefrom 20 atm % to 30 atm %. A content of ruthenium in the ruthenium alloyis preferably set at a value of 60 atm % or higher and 90 atm % orlower.

For forming a ruthenium alloy, it is preferable to use a sputteringmethod. When an alloy is film-formed using a sputtering method, thesputtering methods include a method of using a target made of an alloyof ruthenium and the first metal, a co-sputtering method of sputtering aruthenium target and a first metal target in the same chamber at thesame time, and an intermixing method in which a thin film of the firstmetal is formed in advance, ruthenium is film-formed on the thin film bya sputtering method, and the first metal and the ruthenium are alloyedwith energy of colliding atoms. Use of the co-sputtering method and theintermixing method enables composition of an alloy to be altered. Whenthe intermixing method is employed, it is preferable that, afterruthenium film formation has been finished, heat treatment at atemperature of 400° C. or lower be performed for “planarization” of themixed state of metals.

The second electrodes 910 a and 910 b preferably have a two-layerstructure. When the sides of the second electrodes 910 a and 910 b incontact with the ion conductive layers 909 a and 909 b are made of aruthenium alloy, the sides of the second electrodes 910 a and 910 b incontact with the rectifying layers 908 a and 908 b serve as lowerelectrodes of the rectifying elements. As a metal species, a metalnitride, such as titanium nitride and tantalum nitride, that isdifficult to be oxidized, easy to process, and the work function ofwhich is adjustable by adjusting composition thereof can be used.

Titanium and tantalum may also be used as long as being able to inhibitoxidation at boundary faces of the second electrodes 910 a and 910 bwith the rectifying layers 908 a and 908 b. Titanium nitride, tantalumnitride, titanium, or tantalum is film-formed on the ruthenium alloylayer by a sputtering method in a continuous vacuum process. Whentitanium or tantalum is nitrided, the nitride is film-formed byintroducing nitrogen into a chamber and using a reactive sputteringmethod.

The rectifying layers 908 a and 908 b are layers that have a bipolarrectification effect and have a characteristic in which currentincreases in a non-linear manner with respect to applied voltage. APoole-Frenkel type insulating film, a Schottky type insulating film, athreshold switching type volatile variable-resistance film, or the likecan be used as the rectifying layers 908 a and 908 b. For example, afilm containing any of titanium oxide, tungsten oxide, molybdenum oxide,hafnium oxide, aluminum oxide, zircon oxide, yttrium oxide, manganeseoxide, niobium oxide, silicon nitride, silicon carbonitride, siliconoxide, and amorphous silicon can be used as the rectifying layers 908 aand 908 b. In particular, constituting a stack by stacking amorphoussilicon, silicon nitride, and amorphous silicon in this sequence enablesexcellent non-linearity to be generated. By, by means of interposing asilicon nitride film between amorphous silicon films, causingcomposition of a portion of the silicon nitride film to be brought to astate in which nitrogen is deficient from the stoichiometric ratio andthereby reducing differences in barrier heights with the secondelectrode 910 a and the third electrode 911, it is possible tofacilitate tunneling current to flow to the silicon nitride at the timeof high voltage application. As a result, a non-linear current change isgenerated.

The third electrode 911 is a metal that serves as an upper electrode ofthe rectifying element, and, for example, tantalum, titanium, tungsten,a nitride thereof, or the like can be used for the third electrode 911.In order to make current-voltage characteristics of the rectifyingelement symmetrical in both positive and negative sides, it ispreferable to use the same material as that of the second electrode 910a for the third electrode 911. The third electrode 911 also has afunction as an etching stop layer when the via 919 a is electricallyconnected onto the second electrode 910 a. Thus, it is preferable thatthe third electrode 911 have a low etching rate for plasma of afluorocarbon-based gas that is used in etching of the interlayerinsulating film 915. For forming the third electrode 911, it ispreferable to use a sputtering method. When a metal nitride isfilm-formed using a sputtering method, it is preferable to use areactive sputtering method in which a metal target is vaporized usingplasma of a gas mixture of nitrogen and argon. A metal vaporized fromthe metal target reacts with nitrogen and forms a metal nitride, whichis film-formed on a substrate.

The third electrode 911 is present only on the two-terminal switch 922with a rectifying element in which a rectifying element is formed and isnot present on the three-terminal switch 923.

The first hard mask film 912 is a film that serves as a hard mask filmand a passivation film when the third electrode 911, the secondelectrodes 910 a and 910 b, the rectifying layers 908 a and 908 b, andthe ion conductive layers 909 a and 909 b are etched. For the first hardmask film 912, for example, a silicon nitride film, a silicon oxide filmor the like, or a stack thereof can be used. The first hard mask film912 preferably includes the same material as the protection insulatingfilm 914 and the barrier insulating film 907.

The second hard mask film 913 is a film that serves as a hard mask filmwhen the third electrode 911, the second electrodes 910 a and 910 b, therectifying layers 908 a and 908 b, and the ion conductive layers 909 aand 909 b are etched. For the second hard mask film 913, for example, asilicon nitride film, a silicon oxide film or the like, or a stackthereof can be used.

Based on a shape of the second hard mask film 913, the two-terminalswitch 922 with a rectifying element and the three-terminal switch 923are formed differently from each other. On the barrier insulating film907 of the two-terminal switch 922 with a rectifying element and thethree-terminal switch 923, the ion conductive layers 909 a and 909 b,the second electrodes 910 a and 910 b, the rectifying layers 908 a and908 b, the third electrode 911, the first hard mask film 912, and thesecond hard mask film 913 are film-formed. Subsequently, in a manner inwhich a shape of the second hard mask film 913, formed through tworounds of patterning and etching, is transferred onto the two-terminalswitch 922 with a rectifying element, a rectifying element is formed onthe second electrode 910 a.

That is, a stacked structure for the two-terminal switch 922 with arectifying element is film-formed once on the whole wafer, and, on anelement portion to which the three-terminal switch 923 is to be formed,patterning for forming a rectifying element portion in the two-terminalswitch 922 with a rectifying element is configured not to be performed(a resist is configured not to be left). This configuration causesthickness of a portion of the second hard mask film 913 on thethree-terminal switch 923 to be reduced. Subsequently, performingetching enables a portion of the third electrode 911 on thethree-terminal switch 923 to be removed. That is, an area on thethree-terminal switch 923 is brought into the same condition as an areaon the two-terminal switch 922 with a rectifying element except an areaunder which the rectifying element is formed. The rectifying layer 908 bmay or does not have to remain on the second electrode 910 a of thethree-terminal switch 923. In addition, the first hard mask film 912 andthe second hard mask film 913 do not remain on the three-terminal switch923.

The protection insulating film 914 is an insulating film that hasfunctions of preventing the two-terminal switch 922 with a rectifyingelement and the three-terminal switch 923 from being damaged and furtherpreventing desorption of oxygen from the ion conductive layers 909 a and909 b. For the protection insulating film 914, for example, a siliconnitride film, a silicon carbonitride film or the like can be used. Theprotection insulating film 914 is preferably made of the same materialas the first hard mask film 912 and the barrier insulating film 907. Inthe case of being made of the same material, the protection insulatingfilm 914 is integrated into one body with the barrier insulating film907 and the first hard mask film 912 and adhesiveness of boundary facesthereamong is thereby improved, which enables the four-terminal switch922 with rectifying elements and the two-terminal switch 923 to beprotected more securely.

The interlayer insulating film 915 is an insulating film that is formedon the protection insulating film 914. For the interlayer insulatingfilm 915, for example, a silicon oxide film, a SiOC film or the like canbe used. The interlayer insulating film 915 may be a stack of aplurality of insulating films. The interlayer insulating film 915 may bemade of the same material as the interlayer insulating film 917. In theinterlayer insulating film 915, lower holes for embedding the vias 919 aand 919 b are formed, and, in the lower holes, the vias 919 a and 919 bare embedded with the second barrier metals 920 a and 920 b in between,respectively.

For the low-k insulating film 916, a low dielectric constant film (forexample, a SiOCH film) or the like that has a lower relative dielectricconstant than a silicon oxide film is used. The low-k insulating film916 is an insulating film that is interposed between the interlayerinsulating films 915 and 917 and has a low dielectric constant. In thelow-k insulating film 916, wiring grooves for embedding the secondwirings 918 a and 918 b are formed. In the wiring grooves in the low-kinsulating film 916, the second wirings 918 a and 918 b are embeddedwith the second barrier metals 920 a and 920 b in between, respectively.

The interlayer insulating film 917 is an insulating film that is formedon the low-k insulating film 916. For the interlayer insulating film917, for example, a silicon oxide film, a SiOC film, a low dielectricconstant film (for example, a SiOCH film) that has a lower relativedielectric constant than a silicon oxide film, or the like can be used.The interlayer insulating film 917 may be a stack of a plurality ofinsulating films. The interlayer insulating film 917 may be made of thesame material as the interlayer insulating film 915. In the interlayerinsulating film 917, wiring grooves for embedding the second wirings 918a and 918 b are formed. In the wiring grooves in the interlayerinsulating film 917, the second wirings 918 a and 918 b are embeddedwith the second barrier metals 920 a and 920 b in between, respectively.

The second wirings 918 a and 918 b are wirings that are embedded in thewiring grooves formed in the interlayer insulating film 917 and thelow-k insulating film 916 with the second barrier metals 920 a and 920 bin between, respectively. The second wirings 918 a and 918 b areintegrated into one body with the vias 919 a and 919 b, respectively.

The via 919 a is embedded in the lower hole formed in the interlayerinsulating film 915, the protection insulating film 914, the first hardmask film 912, and the second hard mask film 913 with the second barriermetal 920 a in between. The via 919 b is embedded in the lower holeformed in the interlayer insulating film 915 and the protectioninsulating film 914 with the second barrier metal 920 b in between.

The via 919 a is electrically connected to the third electrode 911 withthe second barrier metal 920 a in between. The via 919 b is electricallyconnected to the second electrode 910 b with the second barrier metal920 b in between. For the second wirings 918 a and 918 b and the vias919 a and 919 b, for example, copper can be used.

The second barrier metals 920 a and 920 b are conductive films thatcover the side surfaces and the bottom surfaces of the second wirings918 a and 918 b and the vias 919 a and 919 b, respectively and have abarrier property. The second barrier metals 920 a and 920 b prevent ametal forming the second wirings 918 a and 918 b (including the vias 919a and 919 b) from diffusing into the interlayer insulating films 915 and917 and lower layers.

For example, when the second wirings 918 a and 918 b and the vias 919 aand 919 b are constituted by metallic elements including copper as amain component, a refractory metal, a nitride thereof, or the like, suchas tantalum, tantalum nitride, titanium nitride, and tungstencarbonitride, or a stacked film thereof can be used for the secondbarrier metals 920 a and 920 b.

The barrier insulating film 921 is an insulating film that is formed onthe interlayer insulating film 917 including the second wirings 918 aand 918 b. The barrier insulating film 921 has roles of preventing themetal (for example, copper) forming the second wirings 918 a and 918 bfrom being oxidized and preventing the metal forming the second wirings918 a and 918 b from diffusing into upper layers. For the barrierinsulating film 921, for example, a silicon carbonitride film, a siliconnitride film, a stacked structure thereof, or the like can be used.

Advantageous Effect of Example Embodiment

According to the present example embodiment, it is possible to achieve asemiconductor device including the two-terminal switch 922 with arectifying element including one rectifying element and thethree-terminal switch 923 provided with no rectifying element in thesame wiring in a multilayer wiring structure. In the present exampleembodiment, it is possible to form the two-terminal switch 922 with arectifying element including two rectifying elements and thethree-terminal switch 923 in the same wiring layer at the same time.

Fifth Example Embodiment

Next, a semiconductor device according to a fifth example embodiment anda method for producing the semiconductor device will be described. Thepresent example embodiment is a semiconductor device that has “athree-terminal switch with a rectifying element and a three-terminalswitch” formed within a multilayer wiring layer. FIG. 13 is across-sectional schematic view illustrating a configuration example ofthe semiconductor device of the fifth example embodiment. The presentexample embodiment is a semiconductor device that includes athree-terminal switch with a rectifying element and a three-terminalswitch within a multilayer wiring layer and the equivalent circuitdiagrams of which are illustrated in (b) of FIG. 16.

Configuration

The semiconductor device illustrated in FIG. 13 has a three-terminalswitch 1022 with a rectifying element and a three-terminal switch 1023within a multilayer wiring layer on a semiconductor substrate 1001.

The multilayer wiring layer has an insulating stacked body in which, onthe semiconductor substrate 1001, an interlayer insulating film 1002, alow-k insulating film 1003, an interlayer insulating film 1004, abarrier insulating film 1007, a protection insulating film 1014, aninterlayer insulating film 1015, a low-k insulating film 1016, aninterlayer insulating film 1017, and a barrier insulating film 1021 arestacked in this sequence. The multilayer wiring layer has, in wiringgrooves formed in the interlayer insulating film 1004 and the low-kinsulating film 1003, first wirings 1005 a and 1005 b embedded withfirst barrier metals 1006 a and 1006 b in between, respectively. Inaddition, the multilayer wiring layer has, in wiring grooves formed inthe interlayer insulating film 1004 and the low-k insulating film 1003,first wirings 1005 c and 1005 d embedded with first barrier metals 1006c and 1006 d in between, respectively.

Further, the multilayer wiring layer has second wirings 1018 a and 1018b embedded in wiring grooves formed in the interlayer insulating film1017 and the low-k insulating film 1016. Furthermore, vias 1019 a and1019 b are embedded in lower holes that are formed in the interlayerinsulating film 1015, the protection insulating film 1014, and a firsthard mask film 1012. Each of pairs of the second wiring 1018 a and thevia 1019 a and the second wiring 1018 b and the via 1019 b areintegrated into one body. In addition, the side surfaces and the bottomsurfaces of pairs of the second wiring 1018 a and the via 1019 a and thesecond wiring 1018 b and the via 1019 b are covered by second barriermetals 1020 a and 1020 b, respectively.

In an opening section formed in the barrier insulating film 1007, on thefirst wirings 1005 a and 1005 b that serve as first electrodes, aportion of the interlayer insulating film 1004 flanked by the firstwirings 1005 a and 1005 b, the wall surface of the opening section inthe barrier insulating film 1007, and the barrier insulating film 1007,an ion conductive layer 1009 a, a second electrode 1010 a, a rectifyinglayer 1008 a, and a third electrode 1011 are stacked in this sequenceand the three-terminal switch 1022 with a rectifying element is therebyformed. In addition, on the third electrode 1011, the first hard maskfilm 1012 and a second hard mask film 1013 are formed. Further, theupper surface and the side face of a stacked body of the ion conductivelayer 1009 a, the second electrode 1010 a, the rectifying layer 1008 a,the third electrode 1011, the first hard mask film 1012, and the secondhard mask film 1013 are covered by the protection insulating film 1014.

The multilayer wiring layer has, in another opening section formed inthe barrier insulating film 1007, on the first wirings 1005 c and 1005 dthat serve as first electrodes, a portion of the interlayer insulatingfilm 1004 flanked by the first wirings 1005 c and 1005 d, the wallsurface of the another opening section in the barrier insulating film1007, and the barrier insulating film 1007, the three-terminal switch1023 formed in which an ion conductive layer 1009 b, a second electrode1010 b, and a rectifying layer 1008 b are stacked in this sequence andthe upper surface and the side face of a stacked body of the ionconductive layer 1009 b and the second electrode 1010 b covered by theprotection insulating film 1014.

Forming portions of the first wirings 1005 a and 1005 b into lowerelectrodes of the three-terminal switch 1022 with a rectifying elementand forming portions of the first wirings 1005 c and 1005 d into lowerelectrodes of the three-terminal switch 1023, while simplifying thenumber of process steps, enable electrode resistance to be reduced. Onlygenerating a mask set of at least three PRs as additional process stepsto a regular copper damascene wiring process enables the three-terminalswitch 1022 with a rectifying element and the three-terminal switch 1023to be provided in the same wiring layer, which enables reduction inelement resistance and cost reduction to be achieved at the same time.

The three-terminal switch 1022 with a rectifying element has the ionconductive layer 1009 a in direct contact with the first wirings 1005 aand 1005 b in regions in the opening section formed in the barrierinsulating film 1007. A metal constituting a portion of the ionconductive layer 1009 a diffuses into the first wirings 1005 a and 1005b and thereby forms alloy layers.

The three-terminal switch 1023 has the ion conductive layer 1009 b indirect contact with the first wirings 1005 c and 1005 d in regions inthe another opening section formed in the barrier insulating film 1007.A metal constituting a portion of the ion conductive layer 1009 bdiffuses into the first wirings 1005 c and 1005 d and thereby formsalloy layers.

The three-terminal switch 1022 with a rectifying element has therectifying layer 1008 a on the second electrode 1010 a, and therectifying layer 1008 a is in contact with the third electrode 1011 atthe upper surface of the rectifying layer 1008 a. On the third electrode1011, the first hard mask film 1012 and the second hard mask film 1013remain. The second hard mask film 1013 does not have to remain.

In the three-terminal switch 1022 with a rectifying element, the via1019 a and the third electrode 1011 are electrically connected to eachother with the second barrier metal 1020 a in between, on the thirdelectrode 1011.

The three-terminal switch 1022 with a rectifying element is on/offcontrolled by applying voltage or flowing current between the secondelectrode 1010 a and the first wiring 1005 a or 1005 b via therectifying layer 1008 a, such as being on/off controlled by use ofelectric field diffusion of metal ions supplied from a metal forming thefirst wirings 1005 a and 1005 b into the ion conductive layer 1009 a. Onthis occasion, on-resistance is determined by current in the rectifyinglayer 1008 a.

The three-terminal switch 1023 has the via 1019 b electrically connectedto the second electrode 1010 b via the second barrier metal 1020 b onthe second electrode 1010 b. The rectifying layer 1008 b may remain onthe second electrode 1010 b or may be removed when etching is performedin a production process of the three-terminal switch 1023. Thethree-terminal switch 1023 is on/off controlled by applying voltage orflowing current, such as being on/off controlled by use of electricfield diffusion of metal ions supplied from a metal forming the firstwirings 1005 c and 1005 d into the ion conductive layer 1009 b.

The semiconductor substrate 1001 is a substrate on which semiconductorelements are formed. For the semiconductor substrate 1001, substrates,such as a silicon substrate, a single crystal substrate, an SOIsubstrate, a TFT substrate, a substrate for liquid crystal production,and the like can be used.

The interlayer insulating film 1002 is an insulating film that is formedon the semiconductor substrate 1001. For the interlayer insulating film1002, for example, a silicon oxide film, a SiOC film or the like can beused. The interlayer insulating film 1002 may be a stack of a pluralityof insulating films.

For the low-k insulating film 1003, a low dielectric constant film (forexample, a SiOCH film) or the like that has a lower relative dielectricconstant than a silicon oxide film is used. The low-k insulating film1003 is an insulating film that is interposed between the interlayerinsulating films 1002 and 1004 and has a low dielectric constant. In thelow-k insulating film 1003, wiring grooves for embedding the firstwirings 1005 a, 1005 b, 1005 c, and 1005 d are formed. In the wiringgrooves in the low-k insulating film 1003, the first wirings 1005 a,1005 b, 1005 c, and 1005 d are embedded with the first barrier metals1006 a, 1006 b, 1006 c, and 1006 d in between, respectively

The interlayer insulating film 1004 is an insulating film that is formedon the low-k insulating film 1003. For the interlayer insulating film1004, for example, a silicon oxide film, a SiOC film or the like can beused. The interlayer insulating film 1004 may be a stack of a pluralityof insulating films. In the interlayer insulating film 1004, wiringgrooves for embedding the first wirings 1005 a, 1005 b, 1005 c, and 1005d are formed. In the wiring grooves in the interlayer insulating film1004, the first wirings 1005 a, 1005 b, 1005 c, and 1005 d are embeddedwith the first barrier metals 1006 a, 1006 b, 1006 c, and 1006 d inbetween, respectively

The first wirings 1005 a and 1005 b are wirings that are embedded in thewiring grooves formed in the interlayer insulating film 1004 and thelow-k insulating film 1003 with the first barrier metals 1006 a and 1006b in between, respectively. The first wirings 1005 a and 1005 b alsoserve as the lower electrodes of the three-terminal switch 1022 with arectifying element and are in direct contact with the ion conductivelayer 1009 a. The upper surface of the ion conductive layer 1009 a is indirect contact with the second electrode 1010 a. As a metal constitutingthe first wirings 1005 a and 1005 b, a metal that can diffuse and beion-conducted in the ion conductive layer 1009 a is used and, forexample, copper or the like can be used. The metal (for example, copper)constituting the first wirings 1005 a and 1005 b may be alloyed withaluminum.

The first wirings 1005 c and 1005 d are wirings that are embedded in thewiring grooves formed in the interlayer insulating film 1004 and thelow-k insulating film 1003 with the first barrier metals 1006 c and 1006d in between, respectively. The first wirings 1005 c and 1005 d alsoserve as the lower electrodes of the three-terminal switch 1023 and arein direct contact with the ion conductive layer 1009 b. The uppersurface of the ion conductive layer 1009 b is in direct contact with thesecond electrode 1010 b. As a metal constituting the first wirings 1005c and 1005 d, a metal that can diffuse and be ion-conducted in the ionconductive layer 1009 b is used and, for example, copper or the like canbe used. The metal (for example, copper) constituting the first wirings1005 c and 1005 d may be alloyed with aluminum.

The first barrier metals 1006 a, 1006 b, 1006 c, and 1006 d areconductive films having a barrier property. The first barrier metals1006 a, 1006 b, 1006 c, and 1006 d, in order to prevent the metalforming the first wirings 1005 a, 1005 b, 1005 c, and 1005 d fromdiffusing into the interlayer insulating film 1004 and lower layers,covers the side surfaces and the bottom surfaces of the respectivewirings. When the first wirings 1005 a, 1005 b, 1005 c, and 1005 d areconstituted by metallic elements including copper as a main component, arefractory metal, a nitride thereof or the like, such as tantalum,tantalum nitride, titanium nitride, and tungsten carbonitride, or astacked film thereof can be used for the first barrier metals 1006 a,1006 b, 1006 c, and 1006 d.

The barrier insulating film 1007 is formed on the interlayer insulatingfilm 1004 including the first wirings 1005 a, 1005 b, 1005 c, and 1005d. This configuration enables the barrier insulating film 1007 to haveroles of preventing the metal (for example, copper) forming the firstwirings 1005 a, 1005 b, 1005 c, and 1005 d from being oxidized,preventing the metal forming the first wirings 1005 a, 1005 b, 1005 c,and 1005 d from diffusing into the interlayer insulating film 1015, andworking as an etching stop layer at the time of processing the thirdelectrode 1011, the rectifying layers 1008 a and 1008 b, the secondelectrodes 1010 a and 1010 b, and the ion conductive layers 1009 a and1009 b. For the barrier insulating film 1007, for example, a SiC film, asilicon carbonitride film, a silicon nitride film, a stacked structurethereof, or the like can be used. The barrier insulating film 1007 ispreferably made of the same material as the protection insulating film1014 and the first hard mask film 1012.

The ion conductive layers 1009 a and 1009 b are films the resistance ofwhich changes. For the ion conductive layers 1009 a and 1009 b, amaterial the resistance of which changes due to action (diffusion, ionicconduction, or the like) of metal ions generated from the metal formingthe first wirings 1005 a, 1005 b, 1005 c, and 1005 d (lower electrodes)can be used. When resistance change in association with switching to anon-state is achieved through deposition of a metal by reduction of metalions, a film capable of conducting ions is used for the ion conductivelayers 1009 a and 1009 b.

The ion conductive layers 1009 a and 1009 b are respectively constitutedby ion conductive layers that are made of a metal oxide and are incontact with the first wirings 1005 a, 1005 b, 1005 c, and 1005 d andion conductive layers that are made of a polymer and are in contact withthe second electrodes 1010 a and 1010 b.

The ion conductive layer made of a polymer in each of the ion conductivelayers 1009 a and 1009 b is formed using a plasma-enhanced CVD method.Raw material of cyclic organosiloxane and helium, which is a carriergas, are flowed into a reaction chamber, and, when the supply of boththe cyclic organosiloxane and helium has stabilized and pressure in thereaction chamber has become constant, application of RF electric poweris started. The amount of supply of the raw material is set at 10 to 200sccm, and 500 sccm helium is supplied via a raw material vaporizer.

The ion conductive layer made of a metal oxide in each of the ionconductive layers 1009 a and 1009 b has a plurality of roles. One roleis to prevent the metal forming the first wirings 1005 a, 1005 b, 1005c, and 1005 d from diffusing into the ion conductive layer made of apolymer due to application of heat and plasma during deposition of theion conductive layer made of a polymer. Another role is to prevent thefirst wirings 1005 a, 1005 b, 1005 c, and 1005 d from being oxidized andbecoming easily accelerated to diffuse into the ion conductive layermade of a polymer. A metal, such as zirconium, hafnium, aluminum andtitanium, that forms the ion conductive layer made of a metal oxide,after film formation of the metal that constitutes the ion conductivelayer made of a metal oxide, is exposed to an oxygen atmosphere underreduced pressure in a film forming chamber for the ion conductive layermade of a polymer and becomes zirconium oxide, hafnium oxide, aluminumoxide, or titanium oxide, thereby becoming a portion of each of the ionconductive layers 1009 a and 1009 b. An optimum thickness of a metalfilm that forms the ion conductive layer made of a metal oxide is 0.5 to1 nm. The metal film that is used for forming the ion conductive layermade of a metal oxide may form a stack or a single layer. Film formationof the metal film that is used for forming the ion conductive layer madeof a metal oxide is preferably performed by sputtering. Metal atoms orions having acquired energy through sputtering plunge and diffuse intothe first wirings 1005 a, 1005 b, 1005 c, and 1005 d and form alloylayers.

The ion conductive layer 1009 a is formed on the first wirings 1005 aand 1005 b, a portion of the interlayer insulating film 1004 flanked bythe first wirings 1005 a and 1005 b, tapered surfaces formed in theopening section in the barrier insulating film 1007, and the barrierinsulating film 1007.

The ion conductive layer 1009 b is formed on the first wirings 1005 cand 1005 d, a portion of the interlayer insulating film 1004 flanked bythe first wirings 1005 c and 1005 d, tapered surfaces formed in theanother opening section in the barrier insulating film 1007, and thebarrier insulating film 1007.

The second electrodes 1010 a and 1010 b are upper electrodes of thethree-terminal switch 1022 with a rectifying element and thethree-terminal switch 1023 and are in direct contact with the ionconductive layers 1009 a and 1009 b, respectively.

For the second electrodes 1010 a and 1010 b, a ruthenium alloycontaining titanium, tantalum, zirconium, hafnium, aluminum or the likeis used. Ruthenium is a metal that is harder to ionize than the metalforming the first wirings 1005 a, 1005 b, 1005 c, and 1005 d and is hardto diffuse and be ion-conducted in the ion conductive layers 1009 a and1009 b. Titanium, tantalum, zirconium, hafnium, or aluminum that isadded to a ruthenium alloy has a good adhesiveness with the metalforming the first wirings 1005 a, 1005 b, 1005 c, and 1005 d. As a firstmetal that constitutes the second electrodes 1010 a and 1010 b and isadded to ruthenium, it is preferable to select a metal that has astandard Gibbs energy of formation of a process of generating metal ionsfrom the metal (oxidation process) larger than ruthenium in the negativedirection. Because of having a standard Gibbs energy of formation of aprocess of generating metal ions from a metal (oxidation process) largerthan ruthenium in the negative direction and being more likely tospontaneously react chemically than ruthenium, titanium, tantalum,zirconium, hafnium, aluminum and the like are highly reactive. For thisreason, in the ruthenium alloy that forms the second electrodes 1010 aand 1010 b, alloying titanium, tantalum, zirconium, hafnium, aluminum orthe like with ruthenium improves adhesiveness thereof with metalcross-links formed by the metal forming the first wirings 1005 a, 1005b, 1005 c, and 1005 d.

On the other hand, an additive metal itself like titanium, tantalum,zirconium, hafnium, aluminum or the like, not alloyed with ruthenium,becomes too highly reactive, which causes a transition to an “OFF” statenot to occur. While a transition from an “ON” state to an “OFF” stateproceeds through oxidation reaction (dissolution reaction) of metalcross-links, when a metal constituting the second electrodes 1010 a and1010 b has a standard Gibbs energy of formation of a process ofgenerating metal ions from the metal (oxidation process) larger, in thenegative direction, than the metal forming the first wirings 1005 a,1005 b, 1005 c, and 1005 d, the oxidation reaction of the metalconstituting the second electrodes 1010 a and 1010 b proceeds fasterthan the oxidation reaction of metal cross-links formed by the metalforming the first wirings 1005 a, 1005 b, 1005 c, and 1005 d, whichcauses a transition to the “OFF” state not to occur.

For this reason, a metal material that is used to form the metalconstituting the second electrodes 1010 a and 1010 b is required to bealloyed with ruthenium that has a standard Gibbs energy of formation ofa process of generating metal ions from the metal (oxidation process)smaller than copper in the negative direction.

Further, when copper, which is a component of metal cross-links, mixeswith the metal constituting the second electrodes 1010 a and 1010 b, aneffect of adding a metal having a large standard Gibbs energy offormation in the negative direction is reduced. For this reason, amaterial having a barrier property against copper and copper ions ispreferable as a metal added to ruthenium. Such materials include, forexample, tantalum and titanium. On the other hand, it has been revealedthat, the larger the amount of additive metal is, the more stable an“ON” state becomes, and even an addition of only 5 atm % metal improvesthe stability. In particular, a case of using titanium as an additivemetal excels in transition to an off-state and stability of an on-state,and it is particularly preferable that an alloy of ruthenium andtitanium be used as the metal constituting the second electrodes 1010 aand 1010 b and a content of titanium be set at a value within a rangefrom 20 atm % to 30 atm %. A content of ruthenium in the ruthenium alloyis preferably set at a value of 60 atm % or higher and 90 atm % orlower.

For forming a ruthenium alloy, it is preferable to use a sputteringmethod. When an alloy is film-formed using a sputtering method, thesputtering methods include a method of using a target made of an alloyof ruthenium and the first metal, a co-sputtering method of sputtering aruthenium target and a first metal target in the same chamber at thesame time, and an intermixing method in which a thin film of the firstmetal is formed in advance, ruthenium is film-formed on the thin film bya sputtering method, and the first metal and the ruthenium are alloyedwith energy of colliding atoms. Use of the co-sputtering method and theintermixing method enables composition of an alloy to be altered. Whenthe intermixing method is employed, it is preferable that, afterruthenium film formation has been finished, heat treatment at atemperature of 400° C. or lower be performed for “planarization” of themixed state of metals.

The second electrodes 1010 a and 1010 b preferably have a two-layerstructure. When the sides of the second electrodes 1010 a and 1010 b incontact with the ion conductive layers 1009 a and 1009 b are made of aruthenium alloy, the sides of the second electrodes 1010 a and 1010 b incontact with the rectifying layers 1008 a and 1008 b serve as lowerelectrodes of the rectifying elements. As a metal species, a metalnitride, such as titanium nitride and tantalum nitride, that isdifficult to be oxidized, easy to process, and the work function ofwhich is adjustable by adjusting composition thereof can be used.

Titanium and tantalum may also be used as long as being able to inhibitoxidation at boundary faces of the second electrodes 1010 a and 1010 bwith the rectifying layers 1008 a and 1008 b. Titanium nitride, tantalumnitride, titanium, or tantalum is film-formed on the ruthenium alloylayer by a sputtering method in a continuous vacuum process. Whentitanium or tantalum is nitrided, the nitride is film-formed byintroducing nitrogen into a chamber and using a reactive sputteringmethod.

The rectifying layers 1008 a and 1008 b are layers that have a bipolarrectification effect and have a characteristic in which currentincreases in a non-linear manner with respect to applied voltage. APoole-Frenkel type insulating film, a Schottky type insulating film, athreshold switching type volatile variable-resistance film, or the likecan be used as the rectifying layers 1008 a and 1008 b. For example, afilm containing any of titanium oxide, tungsten oxide, molybdenum oxide,hafnium oxide, aluminum oxide, zircon oxide, yttrium oxide, manganeseoxide, niobium oxide, silicon nitride, silicon carbonitride, siliconoxide, and amorphous silicon can be used as the rectifying layers 1008 aand 1008 b. In particular, constituting a stack by stacking amorphoussilicon, silicon nitride, and amorphous silicon in this sequence enablesexcellent non-linearity to be generated. By, by means of interposing asilicon nitride film between amorphous silicon films, causingcomposition of a portion of the silicon nitride film to be brought to astate in which nitrogen is deficient from the stoichiometric ratio andthereby reducing differences in barrier heights with the secondelectrode 1010 a and the third electrode 1011, it is possible tofacilitate tunneling current to flow to the silicon nitride at the timeof high voltage application. As a result, a non-linear current change isgenerated.

The third electrode 1011 is a metal that serves as an upper electrode ofthe rectifying element, and, for example, tantalum, titanium, tungsten,a nitride thereof, or the like can be used for the third electrode 1011.In order to make current-voltage characteristics of the rectifyingelement symmetrical in both positive and negative sides, it ispreferable to use the same material as that of the second electrode 1010a for the third electrode 1011. The third electrode 1011 also has afunction as an etching stop layer when the via 1019 a is electricallyconnected onto the second electrode 1010 a. Thus, it is preferable thatthe third electrode 1011 have a low etching rate for plasma of afluorocarbon-based gas that is used in etching of the interlayerinsulating film 1015. For forming the third electrode 1011, it ispreferable to use a sputtering method. When a metal nitride isfilm-formed using a sputtering method, it is preferable to use areactive sputtering method in which a metal target is vaporized usingplasma of a gas mixture of nitrogen and argon. A metal vaporized fromthe metal target reacts with nitrogen and forms a metal nitride, whichis film-formed on a substrate.

The third electrode 1011 is present only on the three-terminal switch1022 with a rectifying element in which a rectifying element is formedand is not present on the three-terminal switch 1023.

The first hard mask film 1012 is a film that serves as a hard mask filmand a passivation film when the third electrode 1011, the secondelectrodes 1010 a and 1010 b, the rectifying layers 1008 a and 1008 b,and the ion conductive layers 1009 a and 1009 b are etched. For thefirst hard mask film 1012, for example, a silicon nitride film, asilicon oxide film or the like, or a stack thereof can be used. Thefirst hard mask film 1012 preferably includes the same material as theprotection insulating film 1014 and the barrier insulating film 1007.

The second hard mask film 1013 is a film that serves as a hard mask filmwhen the third electrode 1011, the second electrodes 1010 a and 1010 b,the rectifying layers 1008 a and 1008 b, and the ion conductive layers1009 a and 1009 b are etched. For the second hard mask film 1013, forexample, a silicon nitride film, a silicon oxide film or the like, or astack thereof can be used.

Based on a shape of the second hard mask film 1013, the three-terminalswitch 1022 with a rectifying element and the three-terminal switch 1023are formed differently from each other. On the barrier insulating film1007 of the three-terminal switch 1022 with a rectifying element and thethree-terminal switch 1023, the ion conductive layers 1009 a and 1009 b,the second electrodes 1010 a and 1010 b, the rectifying layers 1008 aand 1008 b, the third electrode 1011, the first hard mask film 1012, andthe second hard mask film 1013 are film-formed. Subsequently, in amanner in which a shape of the second hard mask film 1013, formedthrough two rounds of patterning and etching, is transferred onto thethree-terminal switch 1022 with a rectifying element, one rectifyingelement is formed on the second electrode 1010 a.

That is, a stacked structure for the three-terminal switch 1022 with arectifying element is film-formed once on the whole wafer, and, on anelement portion to which the three-terminal switch 1023 is to be formed,patterning for forming a rectifying element portion in thethree-terminal switch 1022 with a rectifying element is configured notto be performed (a resist is configured not to be left). Thisconfiguration causes thickness of a portion of the second hard mask film1013 on the three-terminal switch 1023 to be reduced. Subsequently,performing etching enables a portion of the third electrode 1011 on thethree-terminal switch 1023 to be removed. That is, an area on thethree-terminal switch 1023 is brought into the same condition as an areaon the three-terminal switch 1022 with a rectifying element except anarea under which the rectifying element is formed. The rectifying layer1008 b may or does not have to remain on the second electrode 1010 a ofthe three-terminal switch 1023. In addition, the first hard mask film1012 and the second hard mask film 1013 do not remain on thethree-terminal switch 1023.

The protection insulating film 1014 is an insulating film that hasfunctions of preventing the three-terminal switch 1022 with a rectifyingelement and the three-terminal switch 1023 from being damaged andfurther preventing desorption of oxygen from the ion conductive layers1009 a and 1009 b. For the protection insulating film 1014, for example,a silicon nitride film, a silicon carbonitride film or the like can beused. The protection insulating film 1014 is preferably made of the samematerial as the first hard mask film 1012 and the barrier insulatingfilm 1007. In the case of being made of the same material, theprotection insulating film 1014 is integrated into one body with thebarrier insulating film 1007 and the first hard mask film 1012 andadhesiveness of boundary faces thereamong is thereby improved, whichenables the three-terminal switch 1022 with a rectifying element and thethree-terminal switch 1023 to be protected more securely.

The interlayer insulating film 1015 is an insulating film that is formedon the protection insulating film 1014. For the interlayer insulatingfilm 1015, for example, a silicon oxide film, a SiOC film or the likecan be used. The interlayer insulating film 1015 may be a stack of aplurality of insulating films. The interlayer insulating film 1015 maybe made of the same material as the interlayer insulating film 1017. Inthe interlayer insulating film 1015, lower holes for embedding the vias1019 a and 1019 b are formed, and, in the lower holes, the vias 1019 aand 1019 b are embedded with the second barrier metals 1020 a and 1020 bin between, respectively.

For the low-k insulating film 1016, a low dielectric constant film (forexample, a SiOCH film) or the like that has a lower relative dielectricconstant than a silicon oxide film is used. The low-k insulating film1016 is an insulating film that is interposed between the interlayerinsulating films 1015 and 1017 and has a low dielectric constant. In thelow-k insulating film 1016, wiring grooves for embedding the secondwirings 1018 a and 1018 b are formed. In the wiring grooves in the low-kinsulating film 1016, the second wirings 1018 a and 1018 b are embeddedwith the second barrier metals 1020 a and 1020 b in between,respectively.

The interlayer insulating film 1017 is an insulating film that is formedon the low-k insulating film 1016. For the interlayer insulating film1017, for example, a silicon oxide film, a SiOC film, a low dielectricconstant film (for example, a SiOCH film) that has a lower relativedielectric constant than a silicon oxide film, or the like can be used.The interlayer insulating film 1017 may be a stack of a plurality ofinsulating films. The interlayer insulating film 1017 may be made of thesame material as the interlayer insulating film 1015. In the interlayerinsulating film 1017, wiring grooves for embedding the second wirings1018 a and 1018 b are formed. In the wiring grooves in the interlayerinsulating film 1017, the second wirings 1018 a and 1018 b are embeddedwith the second barrier metals 1020 a and 1020 b in between,respectively.

The second wirings 1018 a and 1018 b are wirings that are embedded inthe wiring grooves formed in the interlayer insulating film 1017 and thelow-k insulating film 1016 with the second barrier metals 1020 a and1020 b in between, respectively. The second wirings 1018 a and 1018 bare integrated into one body with the vias 1019 a and 1019 b,respectively.

The via 1019 a is embedded in the lower hole formed in the interlayerinsulating film 1015, the protection insulating film 1014, the firsthard mask film 1012, and the second hard mask film 1013 with the secondbarrier metal 1020 a in between. The via 1019 b is embedded in the lowerhole formed in the interlayer insulating film 1015 and the protectioninsulating film 1014 with the second barrier metal 1020 b in between.

The via 1019 a is electrically connected to the third electrode 1011with the second barrier metal 1020 a in between. The via 1019 b iselectrically connected to the second electrode 1010 b with the secondbarrier metal 1020 b in between. For the second wirings 1018 a and 1018b and the vias 1019 a and 1019 b, for example, copper can be used.

The second barrier metals 1020 a and 1020 b are conductive films thatcover the side surfaces and the bottom surfaces of the second wirings1018 a and 1018 b and the vias 1019 a and 1019 b, respectively and havea barrier property. The second barrier metals 1020 a and 1020 b preventa metal forming the second wirings 1018 a and 1018 b (including the vias1019 a and 1019 b) from diffusing into the interlayer insulating films1015 and 1017 and lower layers.

For example, when the second wirings 1018 a and 1018 b and the vias 1019a and 1019 b are constituted by metallic elements including copper as amain component, a refractory metal, a nitride thereof or the like, suchas tantalum, tantalum nitride, titanium nitride, and tungstencarbonitride, or a stacked film thereof can be used for the secondbarrier metals 1020 a and 1020 b.

The barrier insulating film 1021 is an insulating film that is formed onthe interlayer insulating film 1017 including the second wirings 1018 aand 1018 b. The barrier insulating film 1021 has roles of preventing themetal (for example, copper) forming the second wirings 1018 a and 1018 bfrom being oxidized and preventing the metal forming the second wirings1018 a and 1018 b from diffusing into upper layers. For the barrierinsulating film 1021, for example, a silicon carbonitride film, asilicon nitride film, a stacked structure thereof, or the like can beused.

Advantageous Effect of Example Embodiment

According to the present example embodiment, it is possible to achieve asemiconductor device including the three-terminal switch 1022 with arectifying element including one rectifying element and thethree-terminal switch 1023 provided with no rectifying element in thesame wiring in a multilayer wiring structure. In the present exampleembodiment, it is possible to form the three-terminal switch 1022 with arectifying element including one rectifying element and thethree-terminal switch 1023 in the same wiring layer at the same time.

Sixth Example Embodiment

Next, a semiconductor device according to a sixth example embodiment anda method for producing the semiconductor device will be described. Thepresent example embodiment is a semiconductor device that has “athree-terminal switch with a rectifying element and a two-terminalswitch” formed within a multilayer wiring layer. FIG. 14 is across-sectional schematic view illustrating a configuration example ofthe semiconductor device of the sixth example embodiment. The presentexample embodiment is a semiconductor device that includes athree-terminal switch with a rectifying element and a two-terminalswitch within a multilayer wiring layer and the equivalent circuitdiagrams of which are illustrated in (c) of FIG. 16.

Configuration

The semiconductor device illustrated in FIG. 14 has a three-terminalswitch 1122 with a rectifying element and a two-terminal switch 1123within a multilayer wiring layer on a semiconductor substrate 1101.

The multilayer wiring layer has an insulating stacked body in which, onthe semiconductor substrate 1101, an interlayer insulating film 1102, alow-k insulating film 1103, an interlayer insulating film 1104, abarrier insulating film 1107, a protection insulating film 1114, aninterlayer insulating film 1115, a low-k insulating film 1116, aninterlayer insulating film 1117, and a barrier insulating film 1121 arestacked in this sequence. The multilayer wiring layer has, in wiringgrooves formed in the interlayer insulating film 1104 and the low-kinsulating film 1103, first wirings 1105 a and 1105 b embedded withfirst barrier metals 1106 a and 1106 b in between, respectively. Inaddition, the multilayer wiring layer has, in a wiring groove formed inthe interlayer insulating film 1104 and the low-k insulating film 1103,a first wiring 1105 c embedded with a first barrier metal 1106 c inbetween.

Further, the multilayer wiring layer has second wirings 1118 a and 1118b embedded in wiring grooves formed in the interlayer insulating film1117 and the low-k insulating film 1116. Furthermore, vias 1119 a and1119 b are embedded in lower holes that are formed in the interlayerinsulating film 1115, the protection insulating film 1114, and a firsthard mask film 1112. Each of pairs of the second wiring 1118 a and thevia 1119 a and the second wiring 1118 b and the via 1119 b areintegrated into one body. In addition, the side surfaces and the bottomsurfaces of pairs of the second wiring 1118 a and the via 1119 a and thesecond wiring 1118 b and the via 1119 b are covered by second barriermetals 1120 a and 1120 b, respectively.

In an opening section formed in the barrier insulating film 1107, on thefirst wirings 1105 a and 1105 b that serve as first electrodes, aportion of the interlayer insulating film 1104 flanked by the firstwirings 1105 a and 1105 b, the wall surface of the opening section inthe barrier insulating film 1107, and the barrier insulating film 1107,an ion conductive layer 1109 a, a second electrode 1110 a, a rectifyinglayer 1108 a, and a third electrode 1111 are stacked in this sequenceand the three-terminal switch 1122 with a rectifying element is therebyformed. In addition, on the third electrode 1111, the first hard maskfilm 1112 and a second hard mask film 1113 are formed. Further, theupper surface and the side face of a stacked body of the ion conductivelayer 1109 a, the second electrode 1110 a, the rectifying layer 1108 a,the third electrode 1111, the first hard mask film 1112, and the secondhard mask film 1113 are covered by the protection insulating film 1114.

The multilayer wiring layer has, in another opening section formed inthe barrier insulating film 1107, over the first wiring 1105 c thatserves as a first electrode, the wall surface of the another openingsection in the barrier insulating film 1107, and the barrier insulatingfilm 1107, the two-terminal switch 1123 formed in which an ionconductive layer 1109 b, a second electrode 1110 b, and a rectifyinglayer 1108 b are stacked in this sequence and the upper surface and theside face of a stacked body of the ion conductive layer 1109 b and thesecond electrode 1110 b covered by the protection insulating film 1114.

Forming portions of the first wirings 1105 a and 1105 b into lowerelectrodes of the three-terminal switch 1122 with a rectifying elementand forming a portion of the first wiring 1105 c into a lower electrodeof the two-terminal switch 1123, while simplifying the number of processsteps, enable electrode resistance to be reduced. Only generating a maskset of at least three PRs as additional process steps to a regularcopper damascene wiring process enables the three-terminal switch 1122with a rectifying element and the two-terminal switch 1123 to beprovided in the same wiring layer, which enables reduction in elementresistance and cost reduction to be achieved at the same time.

The three-terminal switch 1122 with a rectifying element has the ionconductive layer 1109 a in direct contact with the first wirings 1105 aand 1105 b in regions in the opening section formed in the barrierinsulating film 1107. A metal constituting a portion of the ionconductive layer 1109 a diffuses into the first wirings 1105 a and 1105b and thereby forms alloy layers.

The two-terminal switch 1123 has the ion conductive layer 1109 b indirect contact with the first wiring 1105 c in a region in the anotheropening section formed in the barrier insulating film 1107. A metalconstituting a portion of the ion conductive layer 1109 b diffuses intothe first wiring 1105 c and thereby forms an alloy layer.

The three-terminal switch 1122 with a rectifying element has therectifying layer 1108 a on the second electrode 1110 a, and therectifying layer 1108 a is in contact with the third electrode 1111 atthe upper surface of the rectifying layer 1108 a. On the third electrode1111, the first hard mask film 1112 and the second hard mask film 1113remain. The second hard mask film 1113 does not have to remain.

In the three-terminal switch 1122 with a rectifying element, the via1119 a and the third electrode 1111 are electrically connected to eachother with the second barrier metal 1120 a in between, on the thirdelectrode 1111.

The three-terminal switch 1122 with a rectifying element is on/offcontrolled by applying voltage or flowing current between the secondelectrode 1110 a and the first wiring 1105 a or 1105 b via therectifying layer 1108 a, such as being on/off controlled by use ofelectric field diffusion of metal ions supplied from a metal forming thefirst wirings 1105 a and 1105 b into the ion conductive layer 1109 a. Onthis occasion, on-resistance is determined by current in the rectifyinglayer 1108 a.

The two-terminal switch 1123 has the via 1119 b electrically connectedto the second electrode 1110 b via the second barrier metal 1120 b onthe second electrode 1110 b. The rectifying layer 1108 b may remain onthe second electrode 1110 b or may be removed when etching is performedin a production process of the two-terminal switch 1123. Thetwo-terminal switch 1123 is on/off controlled by applying voltage orflowing current, such as being on/off controlled by use of electricfield diffusion of metal ions supplied from a metal forming the firstwiring 1105 c into the ion conductive layer 1109 b.

The semiconductor substrate 1101 is a substrate on which semiconductorelements are formed. For the semiconductor substrate 1101, substrates,such as a silicon substrate, a single crystal substrate, an SOIsubstrate, a TFT substrate, a substrate for liquid crystal production,and the like can be used.

The interlayer insulating film 1102 is an insulating film that is formedon the semiconductor substrate 1101. For the interlayer insulating film1102, for example, a silicon oxide film, a SiOC film or the like can beused. The interlayer insulating film 1102 may be a stack of a pluralityof insulating films.

For the low-k insulating film 1103, a low dielectric constant film (forexample, a SiOCH film) or the like that has a lower relative dielectricconstant than a silicon oxide film is used. The low-k insulating film1103 is an insulating film that is interposed between the interlayerinsulating films 1102 and 1104 and has a low dielectric constant. In thelow-k insulating film 1103, wiring grooves for embedding the firstwirings 1105 a, 1105 b, and 1105 c are formed. In the wiring grooves inthe low-k insulating film 1103, the first wirings 1105 a, 1105 b, and1105 c are embedded with the first barrier metals 1106 a, 1106 b, and1106 c in between, respectively

The interlayer insulating film 1104 is an insulating film that is formedon the low-k insulating film 1103. For the interlayer insulating film1104, for example, a silicon oxide film, a SiOC film or the like can beused. The interlayer insulating film 1104 may be a stack of a pluralityof insulating films. In the interlayer insulating film 1104, wiringgrooves for embedding the first wirings 1105 a, 1105 b, and 1105 c areformed. In the wiring grooves in the interlayer insulating film 1104,the first wirings 1105 a, 1105 b, and 1105 c are embedded with the firstbarrier metals 1106 a, 1106 b, and 1106 c in between, respectively

The first wirings 1105 a and 1105 b are wirings that are embedded in thewiring grooves formed in the interlayer insulating film 1104 and thelow-k insulating film 1103 with the first barrier metals 1106 a and 1106b in between, respectively. The first wirings 1105 a and 1105 b alsoserve as the lower electrodes of the three-terminal switch 1122 with arectifying element and are in direct contact with the ion conductivelayer 1109 a. The upper surface of the ion conductive layer 1109 a is indirect contact with the second electrode 1110 a. As a metal constitutingthe first wirings 1105 a and 1105 b, a metal that can diffuse and beion-conducted in the ion conductive layer 1109 a is used and, forexample, copper or the like can be used. The metal (for example, copper)constituting the first wirings 1105 a and 1105 b may be alloyed withaluminum.

The first wiring 1105 c is a wiring that is embedded in the wiringgroove formed in the interlayer insulating film 1104 and the low-kinsulating film 1103 with the first barrier metal 1106 c in between. Thefirst wiring 1105 c also serves as the lower electrode of thetwo-terminal switch 1123 and is in direct contact with the ionconductive layer 1109 b. The upper surface of the ion conductive layer1109 b is in direct contact with the second electrode 1110 b. As a metalconstituting the first wiring 1105 c, a metal that can diffuse and beion-conducted in the ion conductive layer 1109 b is used and, forexample, copper or the like can be used. The metal (for example, copper)constituting the first wiring 1105 c may be alloyed with aluminum.

The first barrier metals 1106 a, 1106 b, and 1106 c are conductive filmshaving a barrier property. The first barrier metals 1106 a, 1106 b, and1106 c, in order to prevent the metal forming the first wirings 1105 a,1105 b, and 1105 c from diffusing into the interlayer insulating film1104 and lower layers, covers the side surfaces and the bottom surfacesof the respective wirings. When the first wirings 1105 a, 1105 b, and1105 c are constituted by metallic elements including copper as a maincomponent, a refractory metal, a nitride thereof or the like, such astantalum, tantalum nitride, titanium nitride and tungsten carbonitride,or a stacked film thereof can be used for the first barrier metals 1106a, 1106 b, and 1106 c.

The barrier insulating film 1107 is formed on the interlayer insulatingfilm 1104 including the first wirings 1105 a, 1105 b, and 1105 c. Thisconfiguration enables the barrier insulating film 1107 to have roles ofpreventing the metal (for example, copper) forming the first wirings1105 a, 1105 b, and 1105 c from being oxidized, preventing the metalforming the first wirings 1105 a, 1105 b, and 1105 c from diffusing intothe interlayer insulating film 1115, and working as an etching stoplayer at the time of processing the third electrode 1111, the rectifyinglayers 1108 a and 1108 b, the second electrodes 1110 a and 1110 b, andthe ion conductive layers 1109 a and 1109 b. For the barrier insulatingfilm 1107, for example, a SiC film, a silicon carbonitride film, asilicon nitride film, a stacked structure thereof, or the like can beused. The barrier insulating film 1107 is preferably made of the samematerial as the protection insulating film 1114 and the first hard maskfilm 1112.

The ion conductive layers 1109 a and 1109 b are films the resistance ofwhich changes. For the ion conductive layers 1109 a and 1109 b, amaterial the resistance of which changes due to action (diffusion, ionicconduction, or the like) of metal ions generated from the metal formingthe first wirings 1105 a, 1105 b, and 1105 c (lower electrodes) can beused. When resistance change in association with switching to anon-state is achieved through deposition of a metal by reduction of metalions, a film capable of conducting ions is used for the ion conductivelayers 1109 a and 1109 b.

The ion conductive layers 1109 a and 1109 b are respectively constitutedby ion conductive layers that are made of a metal oxide and are incontact with the first wirings 1105 a, 1105 b, and 1105 c and ionconductive layers that are made of a polymer and are in contact with thesecond electrodes 1110 a and 1110 b.

The ion conductive layer made of a polymer in each of the ion conductivelayers 1109 a and 1109 b is formed using a plasma-enhanced CVD method.Raw material of cyclic organosiloxane and helium, which is a carriergas, are flowed into a reaction chamber, and, when the supply of boththe cyclic organosiloxane and helium has stabilized and pressure in thereaction chamber has become constant, application of RF electric poweris started. The amount of supply of the raw material is set at 10 to 200sccm, and 500 sccm helium is supplied via a raw material vaporizer.

The ion conductive layer made of a metal oxide in each of the ionconductive layers 1109 a and 1109 b has a plurality of roles. One roleis to prevent the metal forming the first wirings 1105 a, 1105 b, and1105 c from diffusing into the ion conductive layer made of a polymerdue to application of heat and plasma during deposition of the ionconductive layer made of a polymer. Another role is to prevent the firstwirings 1105 a, 1105 b, and 1105 c from being oxidized and becomingeasily accelerated to diffuse into the ion conductive layer made of apolymer. A metal, such as zirconium, hafnium, aluminum and titanium,that forms the ion conductive layer made of a metal oxide, after filmformation of the metal that constitutes the ion conductive layer made ofa metal oxide, is exposed to an oxygen atmosphere under reduced pressurein a film forming chamber for the ion conductive layer made of a polymerand becomes zirconium oxide, hafnium oxide, aluminum oxide, or titaniumoxide, thereby becoming a portion of each of the ion conductive layers1109 a and 1109 b. An optimum thickness of a metal film that forms theion conductive layer made of a metal oxide is 0.5 to 1 nm. The metalfilm that is used for forming the ion conductive layer made of a metaloxide may form a stack or a single layer. Film formation of the metalfilm that is used for forming the ion conductive layer made of a metaloxide is preferably performed by sputtering. Metal atoms or ions havingacquired energy through sputtering plunge and diffuse into the firstwirings 1105 a, 1105 b, and 1105 c and form alloy layers.

The ion conductive layer 1109 a is formed on the first wirings 1105 aand 1105 b, a portion of the interlayer insulating film 1104 flanked bythe first wirings 1105 a and 1105 b, tapered surfaces formed in theopening section in the barrier insulating film 1107, and the barrierinsulating film 1107.

The ion conductive layer 1109 b is formed on the first wiring 1105 c,tapered surfaces formed in the another opening section in the barrierinsulating film 1107, and the barrier insulating film 1107.

The second electrodes 1110 a and 1110 b are upper electrodes of thethree-terminal switch 1122 with a rectifying element and thetwo-terminal switch 1123 and are in direct contact with the ionconductive layers 1109 a and 1109 b, respectively.

For the second electrodes 1110 a and 1110 b, a ruthenium alloycontaining titanium, tantalum, zirconium, hafnium, aluminum or the likeis used. Ruthenium is a metal that is harder to ionize than the metalforming the first wirings 1105 a, 1105 b, and 1105 c and is hard todiffuse and be ion-conducted in the ion conductive layers 1109 a and1109 b. Titanium, tantalum, zirconium, hafnium, or aluminum that isadded to a ruthenium alloy has a good adhesiveness with the metalforming the first wirings 1105 a, 1105 b, and 1105 c. As a first metalthat constitutes the second electrodes 1110 a and 1110 b and is added toruthenium, it is preferable to select a metal that has a standard Gibbsenergy of formation of a process of generating metal ions from the metal(oxidation process) larger than ruthenium in the negative direction.Because of having a standard Gibbs energy of formation of a process ofgenerating metal ions from a metal (oxidation process) larger thanruthenium in the negative direction and being more likely tospontaneously react chemically than ruthenium, titanium, tantalum,zirconium, hafnium, aluminum or the like are highly reactive. For thisreason, in the ruthenium alloy that forms the second electrodes 1110 aand 1110 b, alloying titanium, tantalum, zirconium, hafnium, aluminum orthe like with ruthenium improves adhesiveness thereof with metalcross-links formed by the metal forming the first wirings 1105 a, 1105b, and 1105 c.

On the other hand, an additive metal itself like titanium, tantalum,zirconium, hafnium, aluminum or the like, not alloyed with ruthenium,becomes too highly reactive, which causes a transition to an “OFF” statenot to occur. While a transition from an “ON” state to an “OFF” stateproceeds through oxidation reaction (dissolution reaction) of metalcross-links, when a metal constituting the second electrodes 1110 a and1110 b has a standard Gibbs energy of formation of a process ofgenerating metal ions from the metal (oxidation process) larger, in thenegative direction, than the metal forming the first wirings 1105 a,1105 b, and 1105 c, the oxidation reaction of the metal constituting thesecond electrodes 1110 a and 1110 b proceeds faster than the oxidationreaction of metal cross-links formed by the metal forming the firstwirings 1105 a, 1105 b, and 1105 c, which causes a transition to the“OFF” state not to occur.

For this reason, a metal material that is used to form the metalconstituting the second electrodes 1110 a and 1110 b is required to bealloyed with ruthenium that has a standard Gibbs energy of formation ofa process of generating metal ions from the metal (oxidation process)smaller than copper in the negative direction.

Further, when copper, which is a component of metal cross-links, mixeswith the metal constituting the second electrodes 1110 a and 1110 b, aneffect of adding a metal having a large standard Gibbs energy offormation in the negative direction is reduced. For this reason, amaterial having a barrier property against copper and copper ions ispreferable as a metal added to ruthenium. Such materials include, forexample, tantalum and titanium. On the other hand, it has been revealedthat, the larger the amount of additive metal is, the more stable an“ON” state becomes, and even an addition of only 5 atm % metal improvesthe stability. In particular, a case of using titanium as an additivemetal excels in transition to an off-state and stability of an on-state,and it is particularly preferable that an alloy of ruthenium andtitanium be used as the metal constituting the second electrodes 1110 aand 1110 b and a content of titanium be set at a value within a rangefrom 20 atm % to 30 atm %. A content of ruthenium in the ruthenium alloyis preferably set at a value of 60 atm % or higher and 90 atm % orlower.

For forming a ruthenium alloy, it is preferable to use a sputteringmethod. When an alloy is film-formed using a sputtering method, thesputtering methods include a method of using a target made of an alloyof ruthenium and the first metal, a co-sputtering method of sputtering aruthenium target and a first metal target in the same chamber at thesame time, and an intermixing method in which a thin film of the firstmetal is formed in advance, ruthenium is film-formed on the thin film bya sputtering method, and the first metal and the ruthenium are alloyedwith energy of colliding atoms. Use of the co-sputtering method and theintermixing method enables composition of an alloy to be altered. Whenthe intermixing method is employed, it is preferable that, afterruthenium film formation has been finished, heat treatment at atemperature of 400° C. or lower be performed for “planarization” of themixed state of metals.

The second electrodes 1110 a and 1110 b preferably have a two-layerstructure. When the sides of the second electrodes 1110 a and 1110 b incontact with the ion conductive layers 1109 a and 1109 b are made of aruthenium alloy, the sides of the second electrodes 1110 a and 1110 b incontact with the rectifying layers 1108 a and 1108 b serve as lowerelectrodes of the rectifying elements. As a metal species, a metalnitride, such as titanium nitride and tantalum nitride, that isdifficult to be oxidized, easy to process, and the work function ofwhich is adjustable by adjusting composition thereof can be used.

Titanium and tantalum may also be used as long as being able to inhibitoxidation at boundary faces of the second electrodes 1110 a and 1110 bwith the rectifying layers 1108 a and 1108 b. Titanium nitride, tantalumnitride, titanium, or tantalum is film-formed on the ruthenium alloylayer by a sputtering method in a continuous vacuum process. Whentitanium or tantalum is nitrided, the nitride is film-formed byintroducing nitrogen into a chamber and using a reactive sputteringmethod.

The rectifying layers 1108 a and 1108 b are layers that have a bipolarrectification effect and have a characteristic in which currentincreases in a non-linear manner with respect to applied voltage. APoole-Frenkel type insulating film, a Schottky type insulating film, athreshold switching type volatile variable-resistance film, or the likecan be used as the rectifying layers 1108 a and 1108 b. For example, afilm containing any of titanium oxide, tungsten oxide, molybdenum oxide,hafnium oxide, aluminum oxide, zircon oxide, yttrium oxide, manganeseoxide, niobium oxide, silicon nitride, silicon carbonitride, siliconoxide, and amorphous silicon can be used as the rectifying layers 1108 aand 1108 b. In particular, constituting a stack by stacking amorphoussilicon, silicon nitride, and amorphous silicon in this sequence enablesexcellent non-linearity to be generated. By, by means of interposing asilicon nitride film between amorphous silicon films, causingcomposition of a portion of the silicon nitride film to be brought to astate in which nitrogen is deficient from the stoichiometric ratio andthereby reducing differences in barrier heights with the secondelectrode 1110 a and the third electrode 1111, it is possible tofacilitate tunneling current to flow to the silicon nitride at the timeof high voltage application. As a result, a non-linear current change isgenerated.

The third electrode 1111 is a metal that serves as an upper electrode ofthe rectifying element, and, for example, tantalum, titanium, tungsten,a nitride thereof, or the like can be used for the third electrode 1111.In order to make current-voltage characteristics of the rectifyingelements symmetrical in both positive and negative sides, it ispreferable to use the same material as those of the second electrodes1110 a and 1110 b for the third electrode 1111. The third electrode 1111also has a function as an etching stop layer when the via 1119 a iselectrically connected onto the second electrode 1110 a. Thus, it ispreferable that the third electrode 1111 have a low etching rate forplasma of a fluorocarbon-based gas that is used in etching of theinterlayer insulating film 1115. For forming the third electrode 1111,it is preferable to use a sputtering method. When a metal nitride isfilm-formed using a sputtering method, it is preferable to use areactive sputtering method in which a metal target is vaporized usingplasma of a gas mixture of nitrogen and argon. A metal vaporized fromthe metal target reacts with nitrogen and forms a metal nitride, whichis film-formed on a substrate.

The third electrode 1111 is present only on the three-terminal switch1122 with a rectifying element in which a rectifying element is formedand is not present on the two-terminal switch 1123.

The first hard mask film 1112 is a film that serves as a hard mask filmand a passivation film when the third electrode 1111, the secondelectrodes 1110 a and 1110 b, the rectifying layers 1108 a and 1108 b,and the ion conductive layers 1109 a and 1109 b are etched. For thefirst hard mask film 1112, for example, a silicon nitride film, asilicon oxide film or the like, or a stack thereof can be used. Thefirst hard mask film 1112 preferably includes the same material as theprotection insulating film 1114 and the barrier insulating film 1107.

The second hard mask film 1113 is a film that serves as a hard mask filmwhen the third electrode 1111, the second electrodes 1110 a and 1110 b,the rectifying layers 1108 a and 1108 b, and the ion conductive layers1109 a and 1109 b are etched. For the second hard mask film 1113, forexample, a silicon nitride film, a silicon oxide film or the like, or astack thereof can be used.

Based on a shape of the second hard mask film 1113, the three-terminalswitch 1122 with a rectifying element and the two-terminal switch 1123are formed differently from each other. On the barrier insulating film1107 of the three-terminal switch 1122 with a rectifying element and thetwo-terminal switch 1123, the ion conductive layers 1109 a and 1109 b,the second electrodes 1110 a and 1110 b, the rectifying layers 1108 aand 1108 b, the third electrode 1111, the first hard mask film 1112, andthe second hard mask film 1113 are film-formed. Subsequently, in amanner in which a shape of the second hard mask film 1113, formedthrough two rounds of patterning and etching, is transferred onto thethree-terminal switch 1122 with a rectifying element, one rectifyingelement is formed on the second electrode 1110 a.

That is, a stacked structure for the three-terminal switch 1122 with arectifying element is film-formed once on the whole wafer, and, on anelement portion to which the two-terminal switch 1123 is to be formed,patterning for forming a rectifying element portion in thethree-terminal switch 1122 with a rectifying element is configured notto be performed (a resist is configured not to be left). Thisconfiguration causes thickness of a portion of the second hard mask film1113 on the two-terminal switch 1123 to be reduced. Subsequently,performing etching enables a portion of the third electrode 1111 on thetwo-terminal switch 1123 to be removed. That is, an area on thetwo-terminal switch 1123 is brought into the same condition as an areaon the three-terminal switch 1122 with a rectifying element except anarea under which the rectifying element is formed. The rectifying layer1108 b may or does not have to remain on the second electrode 1110 a ofthe two-terminal switch 1123. In addition, the first hard mask film 1112and the second hard mask film 1113 do not remain on the two-terminalswitch 1123.

The protection insulating film 1114 is an insulating film that hasfunctions of preventing the three-terminal switch 1122 with a rectifyingelement and the two-terminal switch 1123 from being damaged and furtherpreventing desorption of oxygen from the ion conductive layers 1109 aand 1109 b. For the protection insulating film 1114, for example, asilicon nitride film, a silicon carbonitride film or the like can beused. The protection insulating film 1114 is preferably made of the samematerial as the first hard mask film 1112 and the barrier insulatingfilm 1107. In the case of being made of the same material, theprotection insulating film 1114 is integrated into one body with thebarrier insulating film 1107 and the first hard mask film 1112 andadhesiveness of boundary faces thereamong is thereby improved, whichenables the three-terminal switch 1122 with a rectifying element and thetwo-terminal switch 1123 to be protected more securely.

The interlayer insulating film 1115 is an insulating film that is formedon the protection insulating film 1114. For the interlayer insulatingfilm 1115, for example, a silicon oxide film, a SiOC film or the likecan be used. The interlayer insulating film 1115 may be a stack of aplurality of insulating films. The interlayer insulating film 1115 maybe made of the same material as the interlayer insulating film 1117. Inthe interlayer insulating film 1115, lower holes for embedding the vias1119 a and 1119 b are formed, and, in the lower holes, the vias 1119 aand 1119 b are embedded with the second barrier metals 1120 a and 1120 bin between, respectively.

For the low-k insulating film 1116, a low dielectric constant film (forexample, a SiOCH film) or the like that has a lower relative dielectricconstant than a silicon oxide film is used. The low-k insulating film1116 is an insulating film that is interposed between the interlayerinsulating films 1115 and 1117 and has a low dielectric constant. In thelow-k insulating film 1116, wiring grooves for embedding the secondwirings 1118 a and 1118 b are formed. In the wiring grooves in the low-kinsulating film 1116, the second wirings 1118 a and 1118 b are embeddedwith the second barrier metals 1120 a and 1120 b in between,respectively.

The interlayer insulating film 1117 is an insulating film that is formedon the low-k insulating film 1116. For the interlayer insulating film1117, for example, a silicon oxide film, a SiOC film, a low dielectricconstant film (for example, a SiOCH film) that has a lower relativedielectric constant than a silicon oxide film, or the like can be used.The interlayer insulating film 1117 may be a stack of a plurality ofinsulating films. The interlayer insulating film 1117 may be made of thesame material as the interlayer insulating film 1115. In the interlayerinsulating film 1117, wiring grooves for embedding the second wirings1118 a and 1118 b are formed. In the wiring grooves in the interlayerinsulating film 1117, the second wirings 118 a and 118 b are embeddedwith the second barrier metals 1120 a and 1120 b in between,respectively.

The second wirings 1118 a and 1118 b are wirings that are embedded inthe wiring grooves formed in the interlayer insulating film 1117 and thelow-k insulating film 1116 with the second barrier metals 1120 a and1120 b in between, respectively. The second wirings 1118 a and 1118 bare integrated into one body with the vias 1119 a and 1119 b,respectively.

The via 1119 a is embedded in the lower hole formed in the interlayerinsulating film 1115, the protection insulating film 1114, the firsthard mask film 1112, and the second hard mask film 1113 with the secondbarrier metal 1120 a in between. The via 1119 b is embedded in the lowerhole formed in the interlayer insulating film 1115 and the protectioninsulating film 1114 with the second barrier metal 1120 b in between.

The via 1119 a is electrically connected to the third electrode 1111with the second barrier metal 1120 a in between. The via 1119 b iselectrically connected to the second electrode 1110 b with the secondbarrier metal 1120 b in between. For the second wirings 1118 a and 1118b and the vias 1119 a and 1119 b, for example, copper can be used.

The second barrier metals 1120 a and 1120 b are conductive films thatcover the side surfaces and the bottom surfaces of the second wirings1118 a and 1118 b and the vias 1119 a and 1119 b, respectively and havea barrier property. The second barrier metals 1120 a and 1120 b preventa metal forming the second wirings 1118 a and 1118 b (including the vias1119 a and 1119 b) from diffusing into the interlayer insulating films1115 and 1117 and lower layers.

For example, when the second wirings 1118 a and 1118 b and the vias 1119a and 1119 b are constituted by metallic elements including copper as amain component, a refractory metal, a nitride thereof or the like, suchas tantalum, tantalum nitride, titanium nitride and tungstencarbonitride, or a stacked film thereof can be used for the secondbarrier metals 1120 a and 1120 b.

The barrier insulating film 1121 is an insulating film that is formed onthe interlayer insulating film 1117 including the second wirings 1118 aand 1118 b. The barrier insulating film 1121 has roles of preventing themetal (for example, copper) forming the second wirings 1118 a and 1118 bfrom being oxidized and preventing the metal forming the second wirings1118 a and 1118 b from diffusing into upper layers. For the barrierinsulating film 1121, for example, a silicon carbonitride film, asilicon nitride film, a stacked structure thereof, or the like can beused.

Advantageous Effect of Example Embodiment

According to the present example embodiment, it is possible to achieve asemiconductor device including the three-terminal switch 1122 with arectifying element including one rectifying element and the two-terminalswitch 1123 provided with no rectifying element in the same wiring in amultilayer wiring structure. In the present example embodiment, it ispossible to form the three-terminal switch 1122 with a rectifyingelement including one rectifying element and the two-terminal switch1123 in the same wiring layer at the same time.

Preferred example embodiments of the present invention were describedabove, but the present invention is not limited to the above exampleembodiments. It is needless to say that, within the scope of the presentinvention described in the claims, various modifications are possibleand such modifications are also included in the scope of the presentinvention.

All or part of the respective example embodiments described above may bedescribed as in the following supplementary notes, but the presentinvention is not limited thereto.

-   (Supplementary note 1) A semiconductor device comprising

a first switching element and a second switching element that aredisposed in a signal path of a logic circuit, wherein

the first switching element includes a rectifying element and a variableresistance element,

the second switching element does not include the rectifying element andincludes a variable resistance element, and

the first switching element and the second switching element are formedin the same wiring layer.

-   (Supplementary note 2) A semiconductor device comprising

a first switching element and a second switching element that aredisposed in a signal path of a logic circuit, wherein

the first switching element includes two rectifying elements and twovariable resistance elements,

the second switching element does not include the two rectifyingelements and includes the two variable resistance elements, and

the first switching element and the second switching element are formedin the same wiring layer.

-   (Supplementary note 3) A semiconductor device comprising

a first switching element and a second switching element that aredisposed in a signal path of a logic circuit, wherein

the first switching element including two rectifying elements and twovariable resistance elements, wherein each of the two variableresistance elements has two terminals, one terminals of the respectivetwo terminals of the two variable resistance elements are connected toeach other, one terminal and the other terminal of the two otherterminals of the two variable resistance elements are a signal inputterminal and a signal output terminal, respectively, and one electrodeof a first electrode and a second electrode of each of the tworectifying elements is connected to one terminal of the two terminals ofone of the two variable resistance element and the other electrode ofthe first electrode and the second electrode of the rectifying elementserves as a control terminal and

the second switching element including no rectifying element and twovariable resistance elements, wherein each of the two variableresistance elements has two terminals, one terminals of the respectivetwo terminals of the two variable resistance elements are connected toeach other and serve as a common control terminal of the two variableresistance elements and one terminal and the other terminal of the twoother terminals of the two variable resistance elements are a signalinput terminal and a signal output terminal, respectively

are formed in the same wiring layer.

-   (Supplementary note 4) The semiconductor device according to    supplementary note 2 or 3, wherein

film thickness of a metal constituting a common control terminal of thetwo variable resistance elements of the second switching element isthinner than film thickness of a metal constituting a common controlterminal of the two variable resistance elements of the first switchingelement.

-   (Supplementary note 5) The semiconductor device according to any one    of supplementary notes 1 to 4, wherein

on the second switching element, a hard mask film for processing thesecond switching element does not remain.

-   (Supplementary note 6) The semiconductor device according to any one    of supplementary notes 1 to 5, wherein

the rectifying element comprises a rectifying layer that includesamorphous silicon and silicon nitride as main components.

-   (Supplementary note 7) The semiconductor device according to any one    of supplementary notes 1 to 5, wherein

the variable resistance element includes an ion conductive layer inwhich metal ions can move and metal cross-links can be formed.

-   (Supplementary note 8) The semiconductor device according to any one    of supplementary notes 1 to 5, wherein

the variable resistance layer includes a film that is an ion conductorconducting metal ions in accordance with an electric field, thatincludes at least silicon, oxygen, and carbon as main components, andthe relative dielectric constant of which is 2.1 or higher and 3.0 orlower.

-   (Supplementary note 9) A method for producing a semiconductor device    in which a first switching element and a second switching element    are formed at the same time, the first switching element including a    rectifying element and a variable resistance element, the second    switching element including no rectifying element and a variable    resistance element, the method comprising:

film-forming electrodes and a variable resistance layer that form thevariable resistance elements;

film-forming electrodes and a rectifying layer that form the rectifyingelement;

forming a first pattern for constituting the variable resistance elementand the rectifying element to a hard mask for forming the firstswitching element;

forming a second pattern for constituting the variable resistanceelement to a hard mask for forming the second switching element; and

etching the rectifying layer and the variable resistance layer at thesame time by use of the hard masks to which the first pattern and thesecond pattern are formed.

-   (Supplementary note 10) The method for producing the semiconductor    device according to supplementary note 9, wherein

in an area where the first pattern is formed to the hard mask, afterexposure for forming a pattern of the rectifying element to aphotoresist and etching using the photoresist are performed, exposurefor forming a pattern of the variable resistance element to aphotoresist and etching using the photoresist are performed, and

in an area where the second pattern is formed to the hard mask, exposurefor forming a pattern of the rectifying element to a photoresist is notperformed and exposure for forming a pattern of the variable resistanceelement to a photoresist and etching using the photoresist areperformed.

-   (Supplementary note 11) The method for producing the semiconductor    device according to supplementary note 9 or 10, wherein

a first switching element includes two rectifying elements,

the method comprising:

forming a first pattern for constituting the variable resistance elementand the two rectifying elements to the hard mask for forming the firstswitching element; and

etching the rectifying layer and the variable resistance layer at thesame time by use of the hard masks to which the first pattern and thesecond pattern are formed.

-   (Supplementary note 12) The method for producing the semiconductor    device according to any one of supplementary notes 9 to 11, wherein

by etching of the rectifying layer by use of the hard masks to which thefirst pattern and the second pattern are formed, an electrode on therectifying layer positioned in the area where the second switchingelement is formed is removed.

-   (Supplementary note 13) The method for producing the semiconductor    device according to supplementary note 12, wherein

even through etching of the rectifying layer by use of the hard masks towhich the first pattern and the second pattern are formed, therectifying layer positioned in the area where the second switchingelement is formed remains.

The present invention was described above using the example embodimentsdescribed above as exemplary examples. However, the present invention isnot limited to the example embodiments described above. That is, variousmodes that could be understood by a person skilled in the art may beapplied to the present invention within the scope of the presentinvention.

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2016-131469, filed on Jul. 1, 2016, thedisclosure of which is incorporated herein in its entirety by reference.

INDUSTRIAL APPLICABILITY

A variable resistance element used in a semiconductor device of thepresent invention is usable as a non-volatile switching element and, inparticular, suitably usable as a non-volatile switching element thatconstitutes an electronic device, such as a programmable logic and amemory.

REFERENCE SIGNS LIST

122, 822 Four-terminal switch with rectifying elements

123, 923, 1023 Three-terminal switch

722, 922 Two-terminal switch with a rectifying element

723, 823, 1123 Two-terminal switch

1022, 1122 Three-terminal switch with a rectifying element

105 a, 105 b, 105 c, 105 d, 605 a, 605 b, 605 c, 605 d, 705 a, 705 b,805 a, 805 b, 805 c, 905 a, 905 b, 905 c, 1005 a, 1005 b, 1005 c, 1005d, 1105 a, 1105 b, 1105 c First wiring

108 a, 108 b, 608, 608 a, 608 b, 708 a, 708 b, 808 a, 808 b, 908 a, 908b, 1008 a, 1008 b, 1108 a, 1108 b Rectifying layer

109 a, 109 b, 609, 609 a, 609 b, 709 a, 709 b, 809 a, 809 b, 909 a, 909b, 1009 a, 1009 b, 1109 a, 1109 b Ion conductive layer

110 a, 110 b, 610, 610 a, 610 b, 710 a, 710 b, 810 a, 810 b, 910 a, 910b, 1010 a, 1010 b, 1110 a, 1110 b Second electrode

111, 611, 711, 811, 911, 1011, 1111 Third electrode

112, 612, 712, 812, 912, 1012, 1112 First hard mask film

113, 713, 713, 813, 913, 1013, 1113 Second hard mask film

What is claimed is:
 1. A semiconductor device comprising a firstswitching element and a second switching element that are disposed in asignal path of a logic circuit, wherein the first switching elementincludes a rectifying element and a variable resistance element, thesecond switching element does not include the rectifying element andincludes a variable resistance element, and the first switching elementand the second switching element are formed in the same wiring layer. 2.A semiconductor device comprising a first switching element and a secondswitching element that are disposed in a signal path of a logic circuit,wherein the first switching element includes two rectifying elements andtwo variable resistance elements, the second switching element does notinclude the two rectifying elements and includes the two variableresistance elements, and the first switching element and the secondswitching element are formed in the same wiring layer.
 3. Asemiconductor device comprising a first switching element and a secondswitching element that are disposed in a signal path of a logic circuit,wherein the first switching element including two rectifying elementsand two variable resistance elements, wherein each of the two variableresistance elements has two terminals, one terminals of the respectivetwo terminals of the two variable resistance elements are connected toeach other, one terminal and the other terminal of the two otherterminals of the two variable resistance elements are a signal inputterminal and a signal output terminal, respectively, and one electrodeof a first electrode and a second electrode of each of the tworectifying elements is connected to one terminal of the two terminals ofone of the two variable resistance element and the other electrode ofthe first electrode and the second electrode of the rectifying elementserves as a control terminal and the second switching element includingno rectifying element and two variable resistance elements, wherein eachof the two variable resistance elements has two terminals, one terminalsof the respective two terminals of the two variable resistance elementsare connected to each other and serve as a common control terminal ofthe two variable resistance elements and one terminal and the otherterminal of the two other terminals of the two variable resistanceelements are a signal input terminal and a signal output terminal,respectively are formed in the same wiring layer.
 4. The semiconductordevice according to claim 2, wherein film thickness of a metalconstituting a common control terminal of the two variable resistanceelements of the second switching element is thinner than film thicknessof a metal constituting a common control terminal of the two variableresistance elements of the first switching element.
 5. The semiconductordevice according to claim 1, wherein on the second switching element, ahard mask film for processing the second switching element does notremain.
 6. The semiconductor device according to claim 1, wherein therectifying element comprises a rectifying layer that includes amorphoussilicon and silicon nitride as main components.
 7. The semiconductordevice according to claim 1, wherein the variable resistance elementincludes an ion conductive layer in which metal ions can move and metalcross-links can be formed.
 8. The semiconductor device according toclaim 1, wherein the variable resistance layer includes a film that isan ion conductor conducting metal ions in accordance with an electricfield, that includes at least silicon, oxygen, and carbon as maincomponents, and the relative dielectric constant of which is 2.1 orhigher and 3.0 or lower.
 9. A method for producing a semiconductordevice in which a first switching element and a second switching elementare formed at the same time, the first switching element including arectifying element and a variable resistance element, the secondswitching element including no rectifying element and a variableresistance element, the method comprising: forming electrodes and avariable resistance layer that form the variable resistance elements;forming electrodes and a rectifying layer that form the rectifyingelement; forming a first pattern for constituting the variableresistance element and the rectifying element to a hard mask for formingthe first switching element; forming a second pattern for constitutingthe variable resistance element to a hard mask for forming the secondswitching element; and etching the rectifying layer and the variableresistance layer at the same time by use of the hard masks to which thefirst pattern and the second pattern are formed.
 10. The method forproducing the semiconductor device according to claim 9, wherein in anarea where the first pattern is formed to the hard mask, after exposurefor forming a pattern of the rectifying element to a photoresist andetching using the photoresist are performed, exposure for forming apattern of the variable resistance element to a photoresist and etchingusing the photoresist are performed, and in an area where the secondpattern is formed to the hard mask, exposure for forming a pattern ofthe rectifying element to a photoresist is not performed and exposurefor forming a pattern of the variable resistance element to aphotoresist and etching using the photoresist are performed.
 11. Themethod for producing the semiconductor device according to claim 9,wherein a first switching element includes two rectifying elements, themethod comprising: forming a first pattern for constituting the variableresistance element and the two rectifying elements to the hard mask forforming the first switching element; and etching the rectifying layerand the variable resistance layer at the same time by use of the hardmasks to which the first pattern and the second pattern are formed. 12.The method for producing the semiconductor device according to claim 9,wherein by etching of the rectifying layer by use of the hard masks towhich the first pattern and the second pattern are formed, an electrodeon the rectifying layer positioned in the area where the secondswitching element is formed is removed.
 13. The method for producing thesemiconductor device according to claim 12, wherein even through etchingof the rectifying layer by use of the hard masks to which the firstpattern and the second pattern are formed, the rectifying layerpositioned in the area where the second switching element is formedremains.